HONG KONG — Pro-democracy demonstrators in Hong Kong began a new campaign Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June.

Tens of thousands of people marched through parts of the city center Saturday despite a ban on the protest by police. Some protesters gathered around the local government’s headquarters, where they threw bricks and firebombs as police responded with tear gas, pepper spray and water cannons.

On Sunday, demonstrators began congregating at Hong Kong International Airport in a new effort to obstruct access to the critical Asian travel hub. The airport has been off limits to protesters since mid-August, when days of sit-ins led to assaults on two men from mainland China and hundreds of canceled flights.

With classes set to begin Monday for many Hong Kong students, schools could become the next front in the protest movement, which began over widespread anger over an extradition bill that would allow criminal suspects to be taken to mainland China. Since then, demonstrators’ demands have grown to include a call for universal suffrage and an inquiry into accusations of police brutality.

Hundreds of protesters began to converge on the airport Sunday afternoon, traveling by bus, by car and on foot from a nearby subway station. A court injunction obtained after the airport protests last month allows only ticketed passengers and airport employees to enter the main terminals. But demonstrators gathered outside near the entrances, chanting, “Fight for freedom! Stand with Hong Kong.” Some used their cars to block lanes of traffic.

“We have been protesting and occupying for months,” said Daniel Chan, 18, a college student who took a bus to the airport protest. “Still, what we have done seems futile.”

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Chan said he did not intend to do anything illegal, but he was not concerned about the court injunction. “There’s almost nothing left for me to be scared of,” he said. “One document cannot deter me.”

MTR, the Hong Kong subway operator, announced Sunday afternoon that the Airport Express rail service between the airport and the city center was canceled, and trains to the city were later suspended after protesters threw debris on the tracks. Tung Chung Station, the subway stop closest to the airport, was also closed Sunday evening because protesters had damaged the facilities, MTR said.

The protests forced many travelers to find alternative routes to the airport. Nicole Zhao, 38, was one of many who had to wend, dodge and hopscotch their way through barriers that had been set up on the roads.

Zhao, who is from mainland China and works in education, had just landed in Hong Kong from Beijing when she received a notice from the airline suggesting she postpone her trip.

“What the protesters are doing is crazy,” she said. “This just shows how different the Hong Kong and mainland systems are.”

Other travelers were more supportive of the protests.

Eric Jabal, 47, an education consultant, walked with his roller suitcase and suit jacket on a debris-strewn road, dodging protesters and barricades. He said he had left his home at 12:30 p.m. for an 8:50 p.m. flight to Bangalore and had been walking for 25 minutes after he had been dropped off by an Uber.

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But Jabal, a Canadian who has been living in Hong Kong for 25 years, said he didn’t mind the inconvenience.

“I’m really sad,” he said. “That the failure of leadership has led to such profound unrest among such a broad cross section of people — it’s clearly gone beyond the tipping point.”

Students have been a major part of the protests all summer, and the beginning of classes Monday raised questions about whether the start of school would mean a lessening of the movement or whether activism would shift to campuses.

Students have planned two mass assemblies, one in the central business district in the morning and another after school at the Chinese University of Hong Kong. Many high school students have also negotiated with school administrators to participate in sit-ins or set aside classrooms for self-study sessions or silent protests on the first day of school.

Education authorities said students would need parent letters to skip class or to participate in strike activities.

A top government official said Sunday that the administration “steadfastly opposed” the planned class boycotts, calling them extremely irresponsible.

“Schools are places for learning, and are absolutely not places for expressing political views or demands,” Chief Secretary Matthew Cheung wrote in a blog post.

Earlier Sunday, Hong Kong police said they had arrested dozens of people in a subway station that was the scene of some of the most intense violence of the weekend, where officers used clubs and pepper spray on a group of protesters inside a train car.

News footage and videos shared on social media showed members of the police Special Tactical Squad, in dark uniforms with their faces covered, charging into a waiting train car at Prince Edward Station and swinging batons at men and women who cowered on the floor, offering no resistance. After a fury of blows, one officer doused the group in pepper spray and then left.

“The police were out of control,” said Crystal Yip, a 20-year-old college student who was in the station when officers arrived. “They were crazy and they were mad. They were trying to express their anger by attacking people randomly.”

Yolanda Yu, police senior superintendent, said 40 people were arrested in the station on suspicion of unlawful assembly, criminal damages and obstructing officers.

“Protesters used sticks and hard objects to attack police. We used the same level of force to respond to the situation,” Yu said, replying to a reporter asking why police had used pepper spray on commuters who were kneeling on the ground.

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She said police had warned civilians to stay away. “Under chaotic situations, it is indeed hard to determine whether someone is a real journalist, a protester or a violent person,” she said.

The violence in Prince Edward Station began during a dispute between protesters and some older men who were insulting them. One of the men swung a hammer at the protesters, who threw water bottles and umbrellas and later appeared to set off fire extinguishers in the car. After the clashes, the subway system suspended service across much of Hong Kong. Three stations remained closed Sunday.

The subway operator, MTR, has been a target of vandalism since it began suspending service last month to stations in places near where protests are planned. It continued that pattern Saturday, stopping service at Sai Ying Pun Station, near the Chinese government liaison office, a site of some protests.

In the wake of the clashes, Chinese news outlets run by the Communist Party urged the Hong Kong government to take tough steps against the protesters and cited experts urging Carrie Lam, the chief executive of the city, to invoke emergency powers. An online outlet controlled by the Communist Party’s law-and-order committee said the Hong Kong protesters were using “terrorist methods.”

“The chaos in Hong Kong cannot go on!” a front-page editorial in the overseas edition of People’s Daily, the party’s main newspaper, said Sunday. “At this crucial moment, the government of the special administrative region must have the courage and adeptness to apply every legal means to halt the violence and chaos, acting resolutely to detain and arrest violent lawbreakers, applying the law strictly to punish criminals, and swiftly restoring social order.”

An online report from China’s main television broadcaster, CCTV, said that Lam should invoke emergency powers under a colonial-era ordinance to extinguish the violent protests. That step could empower the Hong Kong government to ban demonstrators from wearing masks, speed up arrests and censor “harmful media,” the report said.

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Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators walk in the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators walk in the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Protesters with a wheelbarrow of bricks to throw, during clashes in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Protesters with a wheelbarrow of bricks to throw, during clashes in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Protesters march with a cross and the flags of the United States and colonial Hong Kong, in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Protesters march with a cross and the flags of the United States and colonial Hong Kong, in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators climb over railing to escape police officers outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators climb over railing to escape police officers outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators break a fire hose case at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators break a fire hose case at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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A demonstrator uses a Molotov cocktail during clashes with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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A demonstrator uses a Molotov cocktail during clashes with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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A police officer throws a canister of tear gas during demonstrations in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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A police officer throws a canister of tear gas during demonstrations in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Riot police block a road leading to the official residence of Carrie Lam, Hong Kong’s unpopular chief executive, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong’s central anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Riot police block a road leading to the official residence of Carrie Lam, Hong Kong’s unpopular chief executive, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong’s central anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Seen in reflection, a demonstrator holds a sign showing Carrie Lam, Hong Kong’s unpopular chief executive, during a march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Seen in reflection, a demonstrator holds a sign showing Carrie Lam, Hong Kong’s unpopular chief executive, during a march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Police officers in riot gear behind luggage carts left by pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Police officers in riot gear behind luggage carts left by pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators in the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators in the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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A demonstrator uses a Molotov cocktail during clashes with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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A demonstrator uses a Molotov cocktail during clashes with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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A policeman is offered saline solution by a journalist after inhaling tear gas in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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A policeman is offered saline solution by a journalist after inhaling tear gas in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators climb over a railing at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators climb over a railing at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Demonstrators take cover under umbrellas in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Demonstrators take cover under umbrellas in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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People watch an unauthorized anti-government march from inside a mall in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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People watch an unauthorized anti-government march from inside a mall in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Travelers walk in the streets as pro-democracy demonstrators crowd roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Travelers walk in the streets as pro-democracy demonstrators crowd roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Travelers at Hong Kong International Airport on Sunday, Sept. 1, 2019. Pro-democracy demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Travelers at Hong Kong International Airport on Sunday, Sept. 1, 2019. Pro-democracy demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Travelers look on at pro-democracy demonstrators from inside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Travelers look on at pro-democracy demonstrators from inside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

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Responders try to put out fires during clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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Responders try to put out fires during clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

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A protester dressed as Moses holds a sign with the anti-extradition movement’s five demands in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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A protester dressed as Moses holds a sign with the anti-extradition movement’s five demands in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Riot police hold a line as fires from Molotov cocktails burn near them in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Riot police hold a line as fires from Molotov cocktails burn near them in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

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Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators form a barricade outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators form a barricade outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

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Pro-democracy demonstrators watch a firebomb in the Causeway Bay district of Hong Kong on Saturday, Aug. 31, 2019. The Hong Kong police said on Sunday that they had arrested 40 people involved in the protests. (Laurel Chor/The New York Times)

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Pro-democracy demonstrators watch a firebomb in the Causeway Bay district of Hong Kong on Saturday, Aug. 31, 2019. The Hong Kong police said on Sunday that they had arrested 40 people involved in the protests. (Laurel Chor/The New York Times)

LAUREL CHOR

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators gather in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators gather in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A pro-democracy demonstrator uses a fire extinguisher at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A pro-democracy demonstrator uses a fire extinguisher at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Responders try to put out a fire during clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Responders try to put out a fire during clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A protester marches in the rain near the official residence of Carrie Lam, Hong Kong’s unpopular chief executive, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A protester marches in the rain near the official residence of Carrie Lam, Hong Kong’s unpopular chief executive, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A police officer throws a canister of tear gas during demonstrations in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A police officer throws a canister of tear gas during demonstrations in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Police deploy a water cannon loaded with blue dye, apparently to mark demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police deploy a water cannon loaded with blue dye, apparently to mark demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators form a barricade outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators form a barricade outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Tear gas fills the air around demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Tear gas fills the air around demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Protesters throw a Molotov cocktails at a police barrier outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Protesters throw a Molotov cocktails at a police barrier outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A demonstrator contains a canister of tear gas deployed by riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A demonstrator contains a canister of tear gas deployed by riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators crowd a roadway outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators crowd a roadway outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Riot police surround a prone demonstrator during clashes in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Riot police surround a prone demonstrator during clashes in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police officers in riot gear at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police officers in riot gear at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators march past Hong Kong’s police headquarters, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators march past Hong Kong’s police headquarters, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators behind a barricade of luggage carts at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators behind a barricade of luggage carts at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators gathering for a march hold signs showing Carrie Lam, Hong Kong’s unpopular chief executive, in the Wan Chai district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong’s central anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators gathering for a march hold signs showing Carrie Lam, Hong Kong’s unpopular chief executive, in the Wan Chai district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong’s central anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A protester throws a Molotov cocktail at a police barrier outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A protester throws a Molotov cocktail at a police barrier outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police officers in riot gear at Hong Kong International Airport on Sunday, Sept. 1, 2019. Pro-democracy demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police officers in riot gear at Hong Kong International Airport on Sunday, Sept. 1, 2019. Pro-democracy demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators on a roadway outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators on a roadway outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Police deploy a water cannon during clashes with demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police deploy a water cannon during clashes with demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators form a barricade outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators form a barricade outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A person uses a bullhorn during clashes between demonstrators and riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A person uses a bullhorn during clashes between demonstrators and riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police deploy a water cannon loaded with blue dye, apparently to mark demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police deploy a water cannon loaded with blue dye, apparently to mark demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered anyway, clashing with the police near government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators march past double-decker buses in Hong Kong’s Wan Chai district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators march past double-decker buses in Hong Kong’s Wan Chai district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators behind umbrellas and a barricade of luggage carts at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators behind umbrellas and a barricade of luggage carts at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators move metal barricades at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators move metal barricades at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Riot police surround a demonstrator during clashes in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Riot police surround a demonstrator during clashes in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Protesters shield themselves outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Protesters shield themselves outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police officers in riot gear at Hong Kong International Airport on Sunday, Sept. 1, 2019. Pro-democracy demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police officers in riot gear at Hong Kong International Airport on Sunday, Sept. 1, 2019. Pro-democracy demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators form a barricade on a roadway outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators form a barricade on a roadway outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators with a Molotov cocktail during clashes with riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators with a Molotov cocktail during clashes with riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators walk along the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators walk along the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators gather in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators gather in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators march past Hong Kong’s police headquarters, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators march past Hong Kong’s police headquarters, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators in the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators in the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Protesters protect themselves from tear gas canisters with umbrellas outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Protesters protect themselves from tear gas canisters with umbrellas outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A demonstrator raises a canister of tear gas deployed by riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A demonstrator raises a canister of tear gas deployed by riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Travelers make their way through a line of pro-democracy demonstrators on a road outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Travelers make their way through a line of pro-democracy demonstrators on a road outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators walk in the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators walk in the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A protester throws a Molotov cocktail during clashes in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A protester throws a Molotov cocktail during clashes in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Anti-government marchers carry a banner likening the Chinese flag to the Nazi swastika in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Anti-government marchers carry a banner likening the Chinese flag to the Nazi swastika in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Travelers walk in the streets as pro-democracy demonstrators crowd the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Travelers walk in the streets as pro-democracy demonstrators crowd the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

A police officer aims a rubber bullet gun outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

A police officer aims a rubber bullet gun outside the central government offices in Hong Kong’s Admiralty quarter, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators take cover from riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Police officers in riot gear stand guard at an entrance of Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Police officers in riot gear stand guard at an entrance of Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Pro-democracy demonstrators walk in the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Pro-democracy demonstrators walk in the road after protesting at Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Tear gas fired by riot police spreads amid demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Tear gas fired by riot police spreads amid demonstrators in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands of demonstrators who had been banned from protesting on Saturday gathered anyway, clashing with the police near local government offices and the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Towers seen in reflection during a protest march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Towers seen in reflection during a protest march in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Laurel Chor/The New York Times)

LAUREL CHOR

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Demonstrators clash with riot police in Hong Kong’s Central district, Aug. 31, 2019. Tens of thousands who had been banned from protesting on Saturday gathered in Hong Kong anyway, clashing with the police near the Chinese military headquarters in the most intense day of conflict since the protests began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Clashes between protesters and riot police in Hong Kong’s Central district, Aug. 31, 2019. Crowds of masked protesters in Hong Kong defied official warnings, set fires in the streets and battled the police on Saturday in the most intense clashes since prodemocracy demonstrations here began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Graffiti reading “Freedom!” as pro-democracy demonstrators fill the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI

Graffiti reading “Freedom!” as pro-democracy demonstrators fill the roadways outside Hong Kong International Airport on Sunday, Sept. 1, 2019. Demonstrators in Hong Kong began a new campaign on Sunday to squeeze access to the airport, hours after one of the most tumultuous days since protests in the city began in June. (Lam Yik Fei/The New York Times)

LAM YIK FEI