News channel ABC News spoke to witnesses who said that the shooter first fired several shots from a handgun before tossing smoke bombs and then opening fire again.
The gunman is still on the loose, reported ABC7 Eyewitness News, which showed images of the Borderline Bar and Grill, in Thousand Oaks, California, surrounded by dozens of police vehicles.
Ventura County Sheriff's Capt. Garo Kuredjian said hundreds of people were inside the bar at the time of the shooting.
The bar's website says its hosts "College Country Night" every Wednesday.
A witness told ABC7: 'I was at the front door talking to my stepdad.
The suspect has been described as a Middle Eastern man in his early 20s wearing all black clothing and with a beard.
A sheriff's deputy was among the victims taken to hospital, police confirmed. People threw chairs out of the windows to try to get away. But most agree that there was a shooting and many people fled the bar and grill.
Squad cars and helicopters swarmed the area.
"I can tell you there are at least six victims inside, including a deputy who was injured".
The department advised nearby residents about midnight there was an "ongoing active shooter incident" at Borderline.
Kuredjian and others described Thousand Oaks as a usually placid place.
Thousand Oaks is located forty-five minutes from Los Angeles. "This is something that thankfully is very unusual and it doesn't happen very frequently in our neighborhood".