Authorities said multiple people were injured in the shooting, which took place late on Wednesday night, local time.The extent of the victim's injuries has not yet been released.
"We're still looking for the shooter".
Officers from the Ventura County Sheriff's Office and California Highway Patrol said about 30 shots were fired and several people were injured.
At least six people have been shot, including a deputy sheriff and a doorman, after the shooter stormed in the venue wearing a black trench coat, armed with a "high capacity" gun and smoke grenades.
"I can't tell you what the status of any of those that were shot is at this point", he said.
Several injured in shooting at a bar in southern California in United States, police said.
"It was just some lowlife taking lives he shouldn't be taking", he said.
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Luis Suarez scored twice on Saturday, the second an 89th-minute victor to complete a late comeback against Rayo. "I think we have deserved more. we were more ambitious and we dominated the whole game".
"Multiple injuries reported", the Ventura County Fire Department tweeted. There was a massive law enforcement presence.
One witness saw the suspect tossing smoke bombs in front of the restaurant before watching a security guard get shot.
Borderline Bar & Grill is a western-style facility that hosts theme nights such as country, salsa and swing dancing.
It was college night and country two-step lessons were being offered Wednesday at the Borderline, according to its website.
Witnesses said many of those inside were college students.
No other information was immediately available.