HONG KONG — The videotaped beating of a Hong Kong democracy advocate, apparently by the police, opened a new political fault line in the city on Wednesday, adding to volatile tensions between protesters who have occupied major roads for weeks and the beleaguered government.

The video of the advocate, Ken Tsang, being kicked and beaten in a predawn melee, along with pictures of his bruised body, became an emotion-laden focus for critics of the government after a night of mayhem near the city’s heart. They gave a face to accusations that pro-democracy demonstrators have been targeted by an overzealous police force.

A video filmed by TVB, a usually pro-government television station, showed a bearded man in a black T-shirt being led away by officers in civilian clothes and black police vests, his hands behind him. The video then jumps to a scene in which a man lying on the ground is kicked and hit many times by several figures who appear to be police officers. TVB said the beating had lasted about four minutes.

Outside the North Point Police Station on Wednesday night, Mr. Tsang said he had been “brutally” assaulted by the police during the protest and again at the police station. He said that, because he might pursue legal action, he would not make further comments or answer questions.