Police in Oakland used tear gas and flash grenades on Occupy Oakland protesters, as authorities say a protest involving an estimated 2,000 people turned violent.
About 300 protesters were arrested by the day's end, and city officials said Sunday that arrests from the protests "could reach 400."
Mayor Jean Quan announced at a press conference that the city would seek restitution from the demonstrators. She also demanded that those found guilty be tasked with picking up garbage and removing graffiti in East Oakland.
According to Quan, damage to the City Hall plaza alone has cost more than $2 million since October, reports the Los Angeles Times.
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.
Other demonstrators were arrested earlier in the afternoon, after police said they threw rocks, bottles and other objects at officers and tore down fencing.
The San Francisco Chronicle reported that the event was declared an unlawful assembly after a protester or protesters lobbed a smoke bomb at officers.
Oakland officials say about 250 people were in the group when the protest started on the city's streets around noon Saturday, with demonstrators threatening to take over a vacant building. But KCBS-AM reported the crowd grew to about 2,000 at its height.
The group was being monitored by dozens of Oakland police officers, as well as officers from nearby police agencies. Police began firing tear gas and flash bang grenades as things began to get out of hand. Videos posted to YouTube (warning: graphic language) and other sites captured the scene.
TV station KTVU reported that at least two officers were injured in the melee.
The protest came after Occupy protesters said earlier in the week that they planned to move into a vacant building and turn it into a social center and political hub.
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.
As other officers swept the YMCA, about 100 police officers surrounded City Hall.
"If the cops are willing to defend property over people, I think that shows where the city's priorities are," Carla Orendorff, a UC Davis student, told the Chronicle.
This story has been updated.