The authorities were alerted to the incident at around 11.20pm local time.
USA fire department officials have reported multiple injuries in a shooting at a bar and dance hall in southern California.
Police are responding to reports of a mass shooting at bar in Thousand Oaks, California.
A gunman has opened fire at a country music bar in the city of Thousand Oaks, California, injuring multiple people.
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The Ventura County Fire Department confirmed just after midnight that there had been reports of "multiple injuries" at the bar. Information on the extent of the victims' injuries has not yet been released.
Another witness said he saw a security guard being shot as well as a female cashier, before he also fled.
He said the man set off smoke grenades inside before opening fire.
A police helicopter swirled overhead and officers surrounded the area with cars.
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Officers later reported a man matching the suspect's description on the ground at the scene outside a window.
Firefighters and first responders have arrived on scene and the Ventura County Sheriff's Office is working to secure the scene.
Victims rant to a nearby petrol station to get medical help.
The gunman was still believed to be inside the bar an hour later, according to a police official. An event aimed at university students was scheduled to take place this evening.
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