Oakland police said they arrested about 300 people Saturday as protesters spent a portion of the day trying to get into a vacant convention center, and later broke into City Hall and tried to occupy a YMCA.
Police spokesman Jeff Thomason said most of the arrests came around 8 p.m., when police took many protesters into custody as they marched through the city's downtown, with some entering a YMCA building.
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.
Oakland Mayor Jean Quan during a news briefing late Saturday said protesters had 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 .