At least six people, including one officer, were injured in the shooting the Borderline Bar and Grill at about 23:20 local time on Wednesday.
At least 11 people were shot when a suspect opened fire in the crowded bar in Thousand Oaks, about 50km west of Los Angeles.
Officers from the Ventura County Sheriff's Office and California Highway Patrol said about 30 shots were fired and several people were injured.
The number of potential victims is unclear, but a witness told ABC Los Angeles station KABC-TV that he saw a security guard get shot, and that the alleged shooter appeared to use "a big handgun" and smoke grenades.
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The gunman shouted something, but Ryan could not hear what he said. "These poeple have never hurt anyone in their lives, they are just kids", he said.
"We're still looking for the shooter", Kuredjian said. The suspect reportedly threw smoke bombs inside the bar.
He could not immediately provide information on the extent of the victims' injuries.
A college country night was being held at the venue, which is popular for line dancing. An event aimed at university students was scheduled to take place this evening.