HONG KONG — Hong Kong police moved swiftly Wednesday to enforce China’s new national security rules with the first arrests under the law, as the city immediately felt the chilling effect of Beijing’s offensive to quash dissent in the semiautonomous territory.

The law was proving effective in tamping down the anti-government demonstrations that have wracked Hong Kong for more than a year. On Wednesday, the anniversary of Hong Kong’s return to Chinese control — usually observed by huge pro-democracy marches — a scattered crowd of thousands protested, only to be corralled by police and risk arrest for crimes that did not exist a day earlier.

Deploying pepper spray and water cannons to force protesters off the streets, police arrested about 370 people, including 10 over new offenses created by the security law that takes aim at political activity challenging Beijing. One of the 10 was a 15-year-old girl waving a Hong Kong independence flag, police said.

Far-reaching and punitive, the law threatens the freewheeling cultural scene and civil society that make the fabric of life in Hong Kong so distinct from the rest of China. While officials insist that the law will affect only a small group of offenders, many fear the government could use the law’s expansive definitions to target a wide array of people and organizations, prompting many to take defensive action.

A museum that commemorates the 1989 Tiananmen Square massacre is rushing to digitize its archives, afraid its artifacts could be seized. Booksellers are nervously eyeing customers, worried they could be government spies. Writers have asked a news site to delete more than 100 articles, anxious that old posts could be used against them.

“You can say this law is just targeting protesters and anti-Chinese politicians, but it could be anyone,” said Isabella Ng, a professor at the Education University of Hong Kong who founded a charity that helps refugees in the city.


“Where is the line to draw?” said Ng, who worries that her charity could one day come under scrutiny. “Everything becomes very uncertain.”

The law, which went into effect as soon as it was released Tuesday night, confirmed many residents’ fears that a range of actions that they had previously engaged in had become hazardous. Though the law specifically bans subversion, sedition, terrorism and collusion, its definitions of those crimes could be interpreted broadly to include various forms of speech or organizing.

Lobbying foreign governments or publishing anti-Beijing viewpoints could be punished by life imprisonment in serious cases. So could saying anything seen as undermining the ruling Communist Party’s authority. In the mainland, the party has virtually eliminated independent journalism and imposed onerous restrictions on nongovernmental organizations.

Citing the new law and other factors, the Trump administration is rolling back Hong Kong’s trade privileges with the United States.

“Free Hong Kong was one of the world’s most stable, prosperous and dynamic cities,” Secretary of State Mike Pompeo said at a news conference Wednesday. “Now it’ll be just another communist-run city where its people will be subject to the party elite’s whims.”

Even before the law was passed, activists, journalists, bookshop owners and professors said they had begun second-guessing any speech that could be labeled political. Human rights group Amnesty International said it had drawn up a contingency plan.


Many Hong Kongers have expressed interest in emigration, a task that Britain has promised to make easier. The British foreign secretary, Dominic Raab, said Wednesday that some Hong Kong residents would be allowed to live in Britain for five years — up from six months previously — and then apply for citizenship.

A former British colony, Hong Kong was promised a high degree of autonomy when it returned to Chinese control in 1997. It found success as a bridge between the mainland and the rest of the world, serving as a haven for Chinese dissidents and a base for academics, journalists and researchers to chronicle, unfettered, the country’s modernization.

But reminders of Chinese control were never far away. The abductions of five Hong Kong booksellers in 2015 by mainland authorities rattled others who had openly marketed salacious Chinese political thrillers or modern historical volumes. Though Hong Kong was long a sanctuary for books banned in the mainland, tighter border checks have recently choked the flow of books between Hong Kong and the mainland.

Now the security push has accelerated panic and a sense of foreboding.

“If you haven’t tasted what tyranny is, be prepared, because tyranny is not comfortable,” said Bao Pu, founder of New Century Press, one of the city’s few surviving independent publishers.Albert Wan, co-owner of Bleak House Books, an independent bookstore, said that he closely tracked all his book shipments, regardless of whether they could be considered political, watching for any sign of delay.


He said that he had also grown wary of unfamiliar customers and tries to decide if they are browsing for books or seemingly “building a profile” of him and his employees.

“We are being paranoid,” Wan said. “I don’t know how else to put it.”

For those who built their lives and livelihoods around Hong Kong’s unique freedoms, the security law has forced them to balance two seemingly irreconcilable goals: preserving their own safety, without giving in to fear.

The June 4 Museum, which chronicles Beijing’s bloody military crackdown on student protesters in 1989, has not made plans to move its artifacts overseas for safekeeping. The Chinese government has tried to quash any memory of the massacre, so to hide the archives would be to admit premature defeat, said Lee Cheuk-yan, of the Hong Kong Alliance in Support of Patriotic Democratic Movements in China, which runs the museum.

But reality has also forced the alliance to start an online fundraiser in support of digitizing the museum’s archives, which include video footage of the protests and letters that protesters wrote to their families.

“We of course are racing with time,” Lee said.The chill is not limited to local groups. Large international organizations are also evaluating their future in the city. The new law specifically said that the government would “strengthen the management” of foreign nongovernmental organizations and news agencies.


“The rule of law is going to come under very severe stress in Hong Kong,” said Nicholas Bequelin, director for Amnesty’s East and Southeast Asia operations.

Concerns about the security law’s reach have also forced many writers and protesters to scrutinize their digital footprints for anything that might now be deemed subversive. Activists deleted their accounts on Twitter and on Telegram, a messaging app popular with protesters.

In recent weeks, around a dozen writers asked the editors of InMedia HK, a site that posts articles supporting democracy, to take down some or all of their archives, said Betty Lau, the site’s editor. Editors deleted more than 100 articles, Lau said.

Hong Kong’s reputation for press freedom has long stood in contrast with the mainland’s censorship regime and routine harassment of journalists. But the new security law has thrown the future of the city’s lively news media into question.

The Hong Kong News Executives Association, a group representing the top editors of the city’s major news outlets, expressed concern about the far-reaching effects of the security law before its release. The Foreign Correspondents’ Club urged the government last week to guarantee that authorities would not seek to interfere with the work of reporters. The government has not responded, but officials have sought to reassure the public that the city’s civil liberties will be protected.During a recent end-of-semester meeting at Hong Kong University’s Journalism and Media Studies Center, staff members wondered aloud where the red line would be and whether certain topics would be off-limits, said the center’s director, Keith Richburg.


“I’d be lying if I said I don’t think twice about posting something on Twitter before pushing the button,” said Richburg, a former foreign correspondent with The Washington Post.

One of the starkest indicators that the national security law was already having its intended effect came Tuesday, directly after lawmakers in Beijing unanimously approved it.

Joshua Wong, the 23-year-old who is perhaps Hong Kong’s best-known activist, announced on social media that he would withdraw from Demosisto, the youth political group that he founded in 2016, citing fears for his safety. Demosisto, which has called for greater autonomy for Hong Kong, was for many the face of the protest movement’s future.

Soon after, three other leading members of Demosisto also resigned. A few hours later, the group announced it was disbanding altogether.

In a note explaining his decision, Wong wrote, “Nobody can be sure of their tomorrow.”The crowds of protesters were small Wednesday, relative to the hundreds of thousands that regularly took to the streets last year. But swarms of riot officers quickly surrounded them.

For some protesters, it’s a fight they are willing to continue, even if it means going up against Beijing. “We have to show the people of Hong Kong that we cannot be afraid or deterred by the national security law,” Avery Ng, a leader of the League of Social Democrats, a political party. “We are taking a certain level of risk, being that one of our demands is the end of one-party dictatorship.”