Police fired tear gas and water cannon on Saturday night to disperse protesters who threw petrol bombs and rocks, broke government office windows and blocked a key road near the local headquarters of China's People's Liberation Army.
A series of protests for and against the city's Communist Party rulers in Beijing is planned ahead of the 70th anniversary of the People's Republic on Tuesday, including at the consulate of former colonial power Britain.
Thousands, young and old, gathered peacefully on Saturday at a harbourside park to mark the fifth anniversary of the "Umbrella" pro-democracy movement which gridlocked streets for 79 days in 2014.
Then the violence began, following a pattern of the last few weeks.
Anti-government protesters have attacked the legislature, Beijing's main Liaison Office, occupied the airport, thrown petrol bombs at police, vandalised metro stations and set street fires.
Police have responded with tear gas, water cannon, rubber bullets and occasional live rounds fired into the air.
The protesters are angry about what they see as creeping Chinese interference in Hong Kong, which returned to China in 1997 under a "one country, two systems" formula guaranteeing freedoms that are not enjoyed on the mainland.
China dismisses the accusation and has accused foreign governments, including the United States and Britain, of fanning anti-China sentiment.
Protests were sparked in June by planned legislation, since withdrawn, that would have allowed the extradition of suspected criminals to mainland China. But they have since expanded into a broader pro-democracy movement.