Two officers were injured Saturday night as a California protest over police killings turned violent with protesters smashing windows and throwing rocks and bricks at police, who responded by firing tear gas, authorities said.

Several officers were struck, but there were just two reports of injury, Berkeley police spokeswoman Jenn Coats said.  A Berkeley police officer received hospital treatment for a dislocated shoulder after being hit with a sandbag, while another sustained minor injuries.

The demonstration against police killings of unarmed black men in Missouri and New York began peacefully, the latest of several in the Bay Area in recent days. But Coats said that a some protesters later broke away and began throwing rocks, bottles and pipes at officers.

Dozens of law officers from several surrounding agencies joined Berkeley police in trying to quell the unrest, which included protesters attempting to access Interstate 80 and stop traffic. A California Highway Patrol officer told KTVU that the protesters did not make it onto the freeway and only caused temporary delays.

She said several businesses on University Avenue were vandalized and damaged, including Trader Joe's, Radio Shack and a Wells Fargo Bank branch.

"A small splinter group from the original protests continues to march in Berkeley," Coats said in a statement issued shortly before at 11 p.m. PST. "Unfortunately this group has become violent and continues to throw objects, including rocks and bricks at officers."

She said officers attempting to get the crowd to disperse used tear gas.

"Several dispersal orders have been given, and the crowd has ignored the orders. In response to the violence officers have utilized tear gas and smoke in an effort to disperse the crowd," she said.

Police did not provide further details of any injuries or arrests.

"The total number of arrests and injuries is not known at this time," Coats' statement said.

KTVU reported that approximately 400 people took part in the protest march, which was planned to proceed from the University of California, Berkeley campus to Oakland's Civic Center. The station reported that officers closed two Bay Area Rapid Transit (BART) stations due to the protest, but later re-opened them.

The Associated Press contributed to this report.

Click for more from KTVU.com.