At least 12 people have been killed after a shooter stormed a California bar overnight, the latest in a string US mass shootings in recent years.

The shooting took place Wednesday night at a packed dance club in Thousand Oaks, an affluent Los Angeles suburb with a population of around 130,000.

Authorities on Thursday identified the killer as Ian David Long, 28, a former machine-gunner and combat veteran who apparently took his own life after opening fire in the country music bar.

Ventura County Sheriff Geoff Dean said Mr Long had no criminal record, but that officers had been called to his home in April for a minor disturbance. Long was examined by a mental health specialist at the time.

The former Marine was armed with a Glock 21 .45-caliber handgun, designed to hold 10 rounds plus one in the chamber, according to the sheriff.

A sheriff’s deputy was reported to be among the 12 victims, with more people injured and taken to local hospitals. Malibu-based Pepperdine University said “multiple” students had been on site at the Borderline bar.

Mr Dean described a “horrific scene” with “blood everywhere” at the Borderline Bar and Grill, which describes itself as the area’s largest country dance hall. It was holding one of its regular country music nights for college students on the evening of the shooting.

One witness, speaking on local television, described seeing a man with a “big handgun” and dressed in a black jacket. Another said she saw “smoke everywhere” before fleeing the scene. Other witnesses told media outlets that the gunman first shot a security guard before entering the building.

The shooting comes two weeks after 11 people were killed at a Pittsburgh synagogue in what has been described as the deadliest attack on the Jewish community in US history. That followed a tense week during which more than a dozen mail bombs addressed to prominent critics of President Donald Trump were discovered.

Just over a year ago, 58 people were killed when an attacker opened fire at concertgoers at a resort in Las Vegas.

Mr Trump ordered the US flag to be flown at half-mast at the White House in Washington, as well as across public buildings and military posts, as a mark of respect for the victims of the shooting.

Nancy Pelosi, who will likely lead the incoming Democrat majority in the House of Representatives, said in a statement on Thursday: “The American people deserve real action to end the daily epidemic of gun violence that is stealing the lives of our children on campuses, in places of worship and on our streets. House Democrats will fight to pass bipartisan, commonsense solutions to prevent gun violence in communities across the country.”