About 300 people were arrested Saturday during a chaotic day of Occupy protests that saw demonstrators break into City Hall and burn an American flag, and police fire tear gas and use flash grenades to disperse hundreds of people after some in the crowd threw rocks and bottles and tore down fencing outside a convention center.

It was the most turbulent day of protests since November, when Oakland police forcefully dismantled an Occupy encampment. An exasperated Mayor Jean Quan, who faced heavy criticism for the police action last autumn, called on the Occupy movement to "stop using Oakland as its playground."

Authorities say protesters clashed with police throughout the day, at times throwing rocks, bottles and other objects at officers. The protests grew as the day wore on with an estimated 2,000 demonstrators in the streets at one point.

The national Occupy Wall Street movement, which denounces corporate excess and economic inequality, began in New York City in the fall but has been largely dormant lately.

Oakland, New York and Los Angeles were among the cities with the largest and most vocal Occupy protests early on. The demonstrations ebbed after those cities used force to move out hundreds of demonstrators who had set up tent cities.

In Oakland, the police department received heavy criticism for using force to break up earlier protests. Among the critics was Mayor Jean Quan, who said she wasn't briefed on the department's plans. Earlier this month, a court-appointed monitor submitted a report to a federal judge that included "serious concerns" about the department's handling of the Occupy protests.

Most of the arrests in Oakland came around 8 p.m., when police took about scores of protesters into custody as they marched through the city's downtown, with some entering a YMCA building, police spokesman Jeff Thomason said.

Many other demonstrators were arrested earlier in the afternoon, after police said they threw rocks, bottles and other objects at officers and tore down fencing.

At about the same time police were taking people into custody near the YMCA, about 100 police officers surrounded City Hall, while others swept the inside of the building looking for protesters who had broken into the building, then ran out of the building with American flags before officers arrived.

Quan said that at one point, many forced their way into City Hall, where they burned flags, broke into an electrical box and damaged several art structures, including a recycled art exhibit created by children.

More help from other police agencies was also sent to Oakland, with busloads of Alameda County sheriff's deputies arriving in the downtown area late Saturday.

City Administrator Deanna Santana said protesters pelted officers with bottles, metal pipes, rocks and burning flares and police responded by deploying smoke, tear gas and bean bag rounds.

Police said the group assembled at a downtown plaza Saturday morning, with demonstrators threatening to take over the vacant Henry Kaiser Convention Center. The group then marched through the streets, disrupting traffic.

The crowd grew as the day wore on, with afternoon estimates ranging from about 1,000 to 2,000 people.

The protesters walked to the vacant convention center, where some started tearing down perimeter fencing and "destroying construction equipment" shortly before 3 p.m., police said.

Police said they issued a dispersal order and used smoke and tear gas after some protesters pelted them with bottles, rocks, burning flares and other objects.

Most of the arrests were made when protesters ignored orders to leave and assaulted officers, police said. By 4 p.m., the bulk of the crowd had left the convention center and headed back downtown.

The demonstration comes after Occupy protesters said earlier this week that they planned to move into a vacant building and turn it into a social center and political hub. They also threatened to try to shut down the port, occupy the airport and take over City Hall.

In a statement Friday, Santana said the city would not be "bullied by threats of violence or illegal activity."

Interim police Chief Howard Jordan also warned that officers would arrest those carrying out illegal actions.

Oakland officials said Friday that since the Occupy Oakland encampment was first established in late October, police have arrested about 300 people.