Dozens of police maintained a late-night guard around City Hall following daylong protests that resulted in 300 arrests.

Occupy Oakland demonstrators broke into the historic building and burned a US flag, as officers earlier fired tear gas to disperse people throwing rocks and tearing down fencing at a convention centre.

Saturday’s protests — the most turbulent since Oakland police forcefully dismantled an Occupy encampment in November — came just days after the group said it planned to use a vacant building as a social center and political hub and threatened to try to shut down the port, occupy the airport and take over City Hall.

An exasperated Mayor Jean Quan, who faced heavy criticism for the police action last fall, called on the Occupy movement to “stop using Oakland as its playground.”

“People in the community and people in the Occupy movement have to stop making excuses for this behaviour,” Quan said.

Protesters clashed with police throughout the day, at times throwing rocks, bottles and other objects at officers. And police responded by deploying smoke, tear gas and bean bag rounds.