The extent of the victim's injuries has not yet been released.
Police tell the Ventura County Star that the initial report came around 11:20pm local time (8:20pm NZT) that a man opened fire at the Borderline Bar & Grill in Thousand Oaks, which is about 40 miles west of Los Angeles.
He did say that it was still "a very active scene".
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.More news: Tragedy at Melbourne Cup as horse The CliffsofMoher put down after injury
Another witness said he saw a security guard being shot as well as a female cashier, before he also fled.
A witness told ABC7: 'I was at the front door talking to my stepdad.
The suspect reportedly threw smoke bombs inside the bar.
A Ventura County Sheriff's Office official said approximately 30 shots had been fired inside the building.More news: Rohit Sharma overtakes Virat Kohli; becomes India`s leading run scorer in T20Is
Officers escorted large groups of people to safety as they left the area.
SWAT teams have been pictured trying to surround the restaurant.
They said that soon after the gunman opened fire, victims were running to a nearby petrol station to get help.
Borderline, which bills itself as the "biggest dance floor in town", had been hosting an event called "College Country Night" when the shooting occurred.More news: Mysterious object spotted in solar system may have been an alien probe
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