Twelve people including a police officer were killed by a gunman at a crowded bar in Thousand Oaks, California, late Wednesday, officials said.

Police said several hundred people were inside the venue, which was hosting a "college country night" for students.

Ventura County Sheriff Geoff Dean described the incident at the Borderline Bar and Grill as a "tragic, tragic situation."

Authorities confirmed that the shooter had been killed, but did not immediately identify him. Dean said it was too early to say if there as any link to terrorism.