AT least 12 people were killed in a mass shooting at a college country music night in California last night in the latest deadly attack in the US.

President Donald Trump described the events as “terrible” and praised police officers for their bravery after one of them was killed in the attack.

The shooting started after the gunman shot a doorman before throwing a smoke bomb into the Borderline Bar and Grill in Thousand Oaks, California.

At least 200 people were in the bar which was hosting a university student night. 

Some of those present described having survived a shooting last year when 58 people were killed at a country music festival in Las Vegas as a gunman opened fire from a high-rise hotel room. 

Ventura County Sheriff Geoff Dean described the scene inside the bar as "horrific" and said there was "blood everywhere."

Sergeant Ron Helus died in hospital after being shot as he tried to enter the building.

“He died a hero because he went, he went in to save lives, to save other people’s lives,” Mr Dean said.

The gunman, who has not been identified, was announced dead at the scene and no motive for the attack has been discovered.