The elections were to have taken place on Sunday but Chief Executive Carrie Lam on July 31 postponed them for one year.
Ms Lam blamed an upsurge in coronavirus cases, but critics said her government was worried the opposition would gain seats if voting went ahead on schedule.
Police said that 289 people had been arrested, mostly for unlawful assembly.
One woman was arrested in the Kowloon district of Yau Ma Tei on charges of assault and spreading pro-independence slogans, the police department said on its Facebook page.
It said such slogans are illegal under a newly enacted national security law.
Anti-government protests erupted last year over a proposed extradition law and spread to include demands for greater democracy and criticism of Beijing’s efforts to tighten control over the former British colony.
Coronavirus and the tough new security law have diminished the demonstrations this year, but smaller groups still take to the streets from time to time.
The ruling Communist Party’s decision to impose the law in May prompted complaints it was violating the autonomy promised to the territory when it was returned to China in 1997.
Washington withdrew trading privileges granted to Hong Kong and other governments suspended extradition and other agreements on the grounds that the territory of seven million people is no longer autonomous.
Also on Sunday, police fired pepper balls at protesters in Kowloon’s Mongkok neighbourhood, the South China Morning Post newspaper reported.
In the nearby Jordan neighbourhood, protesters raised a banner criticising the election delay, the Post said.
“I want my right to vote!” activist Leung Kwok-hung, popularly known as Long Hair, was quoted as saying.
The newspaper said Leung was later arrested.
