HONG KONG — Thousands of police officers in riot gear filled the streets of Hong Kong on Sunday, stifling efforts to protest the postponement of legislative elections and China’s imposition of a national security law that gives authorities sweeping new powers to pursue critics.

A large police presence was seen across the Kowloon Peninsula, where some activists had called for a march on the day the elections were initially scheduled to take place. Protesters gathered despite the risk of arrests and fines under social distancing rules that prohibit mass gatherings. Occasional pro-democracy chants broke out as small groups wound through side streets, but the number of demonstrators remained small compared with the huge crowds that gathered last year.

Officers stopped and searched several people and arrested 289 who were suspected of unlawful assembly and other charges, according to police statements. One person was arrested under the National Security Law after chanting a pro-independence slogan, police said.

Activists Figo Chan, Leung Kwok-hung and Raphael Wong of the League of Social Democrats, a leftist pro-democracy group, were among those arrested, according to a post on Chan’s Facebook page. A photographer for a digital news outlet was taken away in a police vehicle, according to his employer, Truth Media Hong Kong.

Video footage captured by reporters showed riot police officers grabbing a girl and pinning her on the ground when she attempted to run away. Police said that officers had used minimum force while chasing the 12-year-old girl and that she was issued a ticket for social distancing violations.

A bus driver who honked while driving past police officers was arrested on suspicion of dangerous driving, according to an officer filming livestream footage for the police Facebook account. Other videos showed plainclothes officers deploying pepper spray at close range and dragging a man across asphalt and sidewalks before putting him in handcuffs.

Police Sunday also arrested an activist accused of “uttering seditious words,” under a little-used, colonial-era sedition law. The activist, Tam Tak-chi, a leading figure in the political group People Power, had organized street booths at which he handed out face masks and delivered criticisms of the government through a loudspeaker.