Kuredjian said he could not confirm whether any of those shot were dead or the severity of their injuries.
Police tell the Los Angeles Times that at least 30 shots were fired at the Borderline Bar & Grill in Thousand Oaks, which is about 40 miles west of Los Angeles.
An unnamed witness told the newspaper that someone ran into the bar around 11.30pm (local time) and started shooting what looked to be a black pistol.
"It was just some lowlife taking lives he shouldn't be taking", he said.
He told reporters: "When our deputies arrive on the scene they attempted to neutralise that threat, I can't tell you if it was neutralised or not".
One witness said there were multiple shots fired inside the bar.
Police have described it as a "mass casualty incident" and helicopters are swirling overhead.
They said that soon after the gunman opened fire, victims were running to a nearby petrol station to get help.
Further information on the extent of the victims' injuries has not been released.
Social media reports claim the suspect shot the bouncer before throwing a smoke grenade and firing more shots.
The bar was hosting a college country music night on Wednesday, according to its website. An event aimed at university students was scheduled to take place this evening.