Multiple people are believed to have been injured in a shooting at a bar packed with college students in southern California, local authorities say.

According to CNN twelve people, including a police officer, were killed after a gunman forced his way into the Borderline Bar & Grill and opened fire on Wednesday night, Sheriff Geoff Dean told reporters moments ago. The suspected gunman was also found dead at the scene. Up to 12 other people are injured.

Ventura County Sheriff Sergeant Eric Buschow confirmed that gunman is dead inside the bar.

Earlier, the Sheriff's Office Captain Garo Kuredjian said at a news conference that the sheriff's deputy was also among the injured and has been taken to a hospital.

Earlier, police told the Los Angeles Times that at least 30 shots were fired at the Borderline Bar & Grill in Thousand Oaks.

Al Jazeera's Rob Reynolds, reporting from Washington, DC, said the bar was packed with college students before the gunman forced his way in.

"The gunman used an automatic weapon and also threw in some sort of smoke bombs into the crowd in the club," he said.

The extent of the victims' injuries has not yet been released. Law enforcement and emergency crews were flooding the scene.

An unnamed source told reporters that a victim managed to escape through the window of the bar.

"He told us how he broke a couple of windows and him and his friends helped push women out to save them first. His hand was cut up and he has blood on his face. His friend was shot in the shoulder," the witness said. 

Authorities urged the public to avoid the area.