After a mostly peaceful day of demonstrations at Occupy Oakland's general strike, incidents Wednesday night and Thursday morning became more violent as protesters clashed with police.
City officials said police responded to a group of protesters who had broken into and occupied a downtown building and set several fires late Wednesday night.
The Occupy Oakland Twitter feed identified the building as the empty Traveler's Aid Society building located at 520 16th Street.
Officials said protesters began hurling rocks, explosives, bottles and flaming objects at officers. Dozens of protesters wielding shields were surrounded and arrested.
Just before midnight the Police Department issued its first order to the crowd to clear the area around the occupied building. Police said they continued to be attacked with rocks, lit flares, roman candles and bottles.
Tear gas and bean bag rounds were fired into the crowd around 12:10 a.m.
Officials said the operation was kept separate from a group of peaceful protesters who remained at Frank Ogawa Plaza.
Protesters had cleared the occupied building by 2:10 a.m., officials said.
Police lines surrounded Frank Ogawa Plaza, but police activity never reached the Occupy Oakland encampment.
Officials also reported there was also a lot of vandalism on private and city buildings. The city's Public Works Agency was scheduled to board up the 16th Street building and other damaged buildings in the Civic Center area.
The Tully's coffee shop at Frank Ogawa Plaza had broken windows and along Broadway graffiti had been sprayed on most buildings by 2 a.m. this morning. Many other areas had been vandalized overnight.