Oakland police fire tear gas, flash grenades on Occupy protesters Oakland police used tear gas and "flash" grenades Saturday to break up an estimated 2,000 Occupy protesters after some demonstrators started throwing objects at officers and tearing down fencing. There were at least 19 arrests, but no reports of serious injuries. Officer Jeff Thomason said police started making arrests when some in the crowd started throwing objects at them. Police declared an unlawful assembly after marchers tore down perimeter fences at the vacant Henry Kaiser Convention Center. Three officers were injured, police said, but did not elaborate. After meeting up at Frank Ogawa Plaza around noon, protesters marched toward the convention center in hopes of making it their new meeting place and social center, NBCBayArea.com reported. Read NBCBayArea.com coverage of the protest Oakland officials said about 250 people were in the group when the protest started but the crowd grew to about 2,000. @OaklandPoliceCA tweeted around 3 p.m., "Area of Oakland Museum and Kaiser Center severely impacted. Persons cutting and tearing fences for entry. Bottles and objects thrown at OPD. During the rally one of the organizers, Shake Anderson, said, "We are here to protect each other and to be civil disobedient. ... We're doing it to change the world, not just today but every day. The protesters were walking through Laney College around 2:30 p.m. Some people were wearing bandanas over their mouths and others were holding signs saying, "We are the 99%." A marching band dressed in pink and black tutus and neon pick tights also was in the crowd. Once they reached the center, organizers planned to kick off a two-day "Oakland Rise-up Festival" to celebrate the establishment of the movement's new space. Occupy Oakland spokesman Leo Ritz-Bar said the group's new headquarters "signals a new direction for the Occupy movement: putting vacant buildings at the service of the community." He also warned that protesters could retaliate against any repressive police action by blocking the Oakland International Airport, occupying City Hall or shutting down the Port of Oakland. City officials said that while they are "committed to facilitating peaceful forms of expression and free speech, police would be prepared to arrest those who break the law. "The city of Oakland will not be bullied by threats of violence or illegal activity," city administrator Deanna Santana said in a statement issued Friday. This article includes reporting from NBCBayArea.com, The Associated Press and msnbc.com staff.