Police say at least six people, including one officer, were injured when gunfire broke out the Borderline Bar and Grill at about 23:20 local time on Wednesday.
"We're still looking for the shooter".
A Ventura County Sheriff's Office official said approximately 30 shots had been fired inside the building.
At least eleven, including a sherrif's deputy, were injured, ABC reported.
"It was just some lowlife taking lives he shouldn't be taking", he said.
Authorities say 11 people including sheriff's deputy shot at Southern California bar; no deaths yet confirmed.
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The witness said the suspect had a handgun and then he also saw the smoke bombs and the guard being shot.
At 11:55pm, law enforcement reported that a California Highway Patrol officer had engaged a suspect and that a man matching the description was down with three gunshot wounds.
The bar is located about 40 miles west of Los Angeles and describes itself as a western-style bar with a spacious dance floor used for theme nights such as country, salsa and swing.
A distraught witness who was inside the bar with his stepson during the shooting told KABC-TV those inside the venue were mostly teens.
It was college night and country two-step lessons were being offered Wednesday at the Borderline, according to its website. "From what I heard, the gunman started shooting at the front desk". More information will be provided as it becomes available.