Police arrested around 300 Occupy protesters in Oakland after trying to enter the City Hall and a convention centre.
Police fired tear gas and smoke grenades to disperse crowds who threw rocks, bottles and other objects.
Oakland was the scene of similar clashes last October. In December, protesters occupied the port.
Oakland is one of several US cities to see mass protests over economic inequality and corporate greed.
The movement began with Occupy Wall Street in New York last year and has since spread.
The local offshoot, Occupy Oakland, had earlier called on protesters to join a weekend of action, saying 28 January would be “Move-in Day”, and they would “occupy a large, vacant building and convert it into a social center”.
The protest march – joined by as many as 2,000 people over the course of the day – moved first to the empty Henry Kaiser convention centre, police said.
Some started tearing down perimeter fencing and “destroying construction equipment”, the Associated Press quotes the police as saying.
When protesters ignored an order to leave, they were dispersed using tear gas and smoke, police added. In response, officers were pelted with bottles, rocks, burning flames and other objects.
Demonstrators also broke into City Hall and a nearby YMCA building in the centre of Oakland, police said.
One post on Occupy Oakland’s Twitter feed later read: “We didn’t get in the building, but fought like our future depended on it.”
Oakland police said in a statement that, while the city “welcomes peaceful forms of assembly and freedom of speech… acts of violence, property destruction and overnight lodging will not be tolerated”.