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.
Unconfirmed reports say the shooter is still at large and that police are still working to secure the scene at the Borderline Bar & Grill.
At least 11 people were injured after a gunman opened fire at a crowded country music bar in the Los Angeles area on Wednesday (Nov 7) night.
Terrified people hid under tables and others smashed windows open with chairs to escape.
The Ventura County Sheriff's Office reports at least 11 people shot, including a deputy responding to the scene. The alleged perpetrator then threw smoke bombs into the bar and continued shooting.
"A gentleman walked in the front door and shot the girl that was behind the counter".
The bar's website says its hosts "College Country Night" every Wednesday.
He said the gunman had a beard, wore a hat, had a black jacket and may have had glasses.
A sheriff's deputy was among the victims taken to hospital, police confirmed.
Nick Steinwender, student body president at nearby California Lutheran University, rushed to the scene when he heard about a shooting at the bar where he knew friends and fellow students were inside.
Squad cars and helicopters swarmed the area.
"I can't tell you much about the shooter at this point".
"Ongoing active shooter incident reported at Borderline", the Ventura County Fire Department tweeted. The city has been named in the past as one of the best places to live in Southern California. "This is something that thankfully is very unusual and it doesn't happen very frequently in our neighborhood".