A gunman shot three people dead and wounded several others at a bar in the US state of California on Wednesday, police said.

The shooter also died in the incident, with police saying there was an "officer-involved shooting" at the location but that no officers had been injured.

"Confirmed 4 deceased at scene, inc. the shooter," the Orange County Sheriff said on social media. "6 transported to hospitals, 5 reported (with) gunshot wounds."

The incident is the latest gun violence to hit the United States, a country where tens of thousands of people die every year from firearms.

The shooting took place at the Cook's Corner bar, a venue popular with bikers, around 45 miles (72 kilometers) southeast of Los Angeles.

The Orange County Register, citing sources, said the incident was sparked by a domestic dispute.

The paper said the gunman was a former law enforcement officer.

The Los Angeles Times, citing sources, said the gunman was a retired officer from Ventura County, north of Los Angeles.

One man interviewed by ABC7 said he had friends in the bar who were unscathed.

"They're upset, of course. They were right next to the shooter. They said it's an older man with a gray beard," he told the news outlet.

Footage broadcast on local television stations showed at least three bodies covered by sheets outside the bar.

One body was on the street, one in the parking lot and another at the back of the bar.

Motorcyclist Gus Gunderman, from nearby Tustin, wrote on Facebook that he had been at the bar earlier in the evening and had left just before the violence erupted.

"Glad to be home safe. I left there not too long ago, like minutes before. Apparently it was soon enough."

Guns exact a hefty toll on the United States every year, but calls to further restrict their ownership or use have been resisted by politicians.

Polls show overwhelming popular support for a blanket rule requiring that anyone purchasing a firearm be checked for a criminal record.

Republicans in Congress argue, however, that this impinges on the constitutional right to own weapons and should be left up to individual states to decide.