Riot police set up a cordon line on Luen Yan Street on Sunday afternoon after dozens of protesters on a march in Tsuen Wan scattered bamboo sticks on the other end of the street, blocking traffic.
Shortly before 5pm, police unfurled yellow flags, warning protesters that they were breaching the law and could face prosecution.
The protesters were among tens of thousands of people who took part in an anti-extradition march from Kwai Fong to Tsuen Wan Park, where a rally is planned.
They moved water barriers from the middle of the road to make more space for marchers, who carried huge banners calling for protesters' five key demands to be met.
The demands are: complete withdrawal of the extradition bill; an independent probe into allegations of police brutality; retraction of the classification of June 12 protesters as rioters; an amnesty for arrested protesters; and political reform to bring true universal suffrage.
Ahead of the event, riot police were called in to help close Kwai Fong MTR station.
Scuffles broke out after some people refused to leave the station, and district councillor Roy Tam says his assistant was arrested.
Police eventually closed the station and pulled down shutters despite complaints that it's a major access point for the area.
The rally organiser, Yu Ngai-ming, has condemned the MTR's handling of the matter, saying he was disappointed at the way the company had handled the matter, saying it hadn't considered the needs of the participants or the Hong Kong public.
Another marcher, called Ma, also questioned the reasoning behind the MTR's decision.
"I really don't understand the logic and I'm very angry," Ma said.
Last updated: 2019-08-25 HKT 17:05