OAKLAND — Occupy Oakland protesters broke into City Hall, stole an American flag from the City Council chamber and set it on fire Saturday night, punctuating a wild day in which police deployed tear gas, arrested more than 400 marchers and dodged hurling objects.

Demonstrators spent the day trying to break into a convention center and temporarily occupying City Hall and a YMCA, all the while snaking around lines of riot-clad police periodically shooting bean bag projectiles, among other uses of nonlethal force.

Saturday marked the first major clashes between protesters and police since November and left three officers with minor injuries, as protesters threw bottles, metal pipes, rocks, spray cans and “improvised explosive devices,” police said.

Late Saturday, paramedics wheeled a pregnant protester away from Frank H. Ogawa Plaza after witnesses said she was hit in the kidney by a police baton. She yelled: “Police did this to me!”

Oakland Mayor Jean Quan spoke moments after the City Hall invasion, saying the city would ask for “stay away” orders against many of the protesters who have repeatedly been arrested in Oakland.

“This particular faction of Occupy … they’re very violent and I’m going to be asking for a lot more mutual aid,” Quan said, adding that the weekly marches prevent the city’s police force from patrolling other parts of Oakland. “They are hurting the neighborhoods by continuing to do this on Saturday nights.”

Oakland police had to ignore 200 lower priority calls for service Saturday night, more than the normal 60 because resources were tied up with the Occupy protests, Sgt. Christopher Bolton said.

The first large skirmish of the day took place on the front steps of the Oakland Museum of California. Police arrested 19 marchers during that confrontation.

Later, about 100 protesters were arrested after police ordered them to disperse at the YMCA on Broadway, police said.

The rest of the marchers headed to City Hall, broke into the building and left with at least two American flags, which were quickly burned. Police regained control of the building, arrested more and guarded the trashed lobby.

The events followed a week where Occupy Oakland organizers announced plans to take over a vacant building to create the movement’s headquarters, with plans for a two-day party. Police and city officials vowed not to allow it.

In what has become a weekly march, about 250 protesters gathered around noon at Frank H. Ogawa Plaza for a rally. At 1:30 p.m., the group began marching with a crowd of about 450 protesters. Forty-five minutes later, some of the marchers entered the campus of Laney College, city officials said.

That was when police first fired tear gas, a witness said.

At 2:50 p.m., marchers began tearing down perimeter fences around the vacant Henry J. Kaiser Convention Center, city officials said. Police declared an unlawful assembly and fired more tear gas. Witnesses said police fired rubber bullets after protesters began hurling items at them.

Sixteen of the protesters were arrested in that confrontation at 10th and Oak streets, mostly for failure to disperse and assaulting a police officer. The three other arrests were scattered along the march route, a police source said.

The most seriously injured officer received a cut to his face that required stitches after a protester hit him with a bicycle. The other two injured officers received bruises, and one injured his hand, the police source said.

Police closed numerous streets around the convention center. Protesters vandalized three private vehicles, police said.

“Their intent is to commit vandalism and cause problems,” interim police Chief Howard Jordan said of the protesters. “Their intent is not to be peaceful.”

By 4 p.m., most of the Occupy crowd, which had grown to about 500, returned to Frank H. Ogawa Plaza. After regrouping, the marchers headed out again and congregated at the Oakland YMCA.

About 6:30 p.m., police ordered protesters to disperse and those who remained were arrested, with some hiding in the YMCA building. As police processed the 100 or so arrested protesters, the rest of the demonstrators headed to City Hall, where they broke into the lobby.

The police department received heavy criticism late last year for breaking up earlier protests, including from the mayor. 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.

Oakland police received mutual aid throughout the day from the Alameda County Sheriff’s Office and city police, including Fremont, Hayward, Berkeley, Pleasanton, Union City and Newark.

Staff writer Jane Tyska and the Associated Press contributed to this report.