Police fired tear gas and pepper spray during clashes with protesters in Hong Kong's Yuen Long area on Saturday night, Radio Television Hong Kong reported.
Protesters blocked roads and set fires earlier in the evening, with clashes continuing until the early hours of Sunday morning.
Yuen Long District Council chairman Zachary Wong Wai-yin was briefly detained before being released, councillor Tommy Cheung Sau-yin wrote in a series of Facebook posts.
The protest at a subway station was held to mark an incident at the site eight months ago when a pro-democracy demonstration was targeted by gangs of men, who attacked activists, lawmakers and train passengers with clubs, leaving dozens injured. Police have been criticized for responding slowly to emergency calls that night.
Saturday's police action was the first time they have used tear gas to disperse protesters since a Feb. 29 rally in Mong Kok.