Six people were shot and killed Sunday in California, with 12 more injured in the latest mass casualty event to spark calls in the United States for new actions to combat gun violence.

The shooting occurred Sunday morning in the California capital city of Sacramento around 2:00 AM after a "large fight" broke out in its downtown area, Police Chief Kathy Lester said at a press conference.

Officers on patrol nearby heard the gunshots and saw people running, she said.

Upon arriving at the scene, "they encountered a large crowd and multiple gunshot victims."

Despite attempts at resuscitation, six victims were pronounced dead at the scene -- three men and three women, all adults, Lester said.

Twelve others were hit by gunfire and are being treated in local hospitals.

At a press conference Sunday morning, Sacramento Mayor Darrell Steinberg described some of the hospitalized as "seriously and critically injured."

He also called on anyone with information to contact authorities or submit evidence via a scannable QR code.

Lester said Sunday evening there were "multiple shooters" and a "stolen handgun" had been recovered at the scene.

She added that investigators had already received multiple videos and tips from members of the public, but were urgently seeking more information.

A video posted online Sunday appeared to show people scuffling in the street, then starting to run as gunfire can be heard.

AFP could not verify the footage, and it was not known if there was a direct relation, but local police said they were aware of the video.

"It was just horrific," said community activist Berry Accius, who arrived minutes after the shooting.

"Just as soon as I walked up you saw a chaotic scene, police all over the place, victims with blood all over their bodies, folks screaming, folks crying, people going, 'Where is my brother?' Mothers crying and trying to identify who their child was," he told local broadcaster KXTV.

The shooting happened in the downtown area, just blocks from the state capitol and close to the venue where the NBA's Sacramento Kings play.

'We must act' 

"America once again mourns for another community devastated by gun violence," said US President Joe Biden in a statement Sunday night.

"We must do more than mourn; we must act," stated Biden, who reiterated his call for Congress to pass legislation to strengthen restrictions on guns.

Mayor Steinberg said it was difficult to find the right words to describe the tragedy.

"The numbers of dead and wounded are difficult to comprehend," he said, adding that he was waiting for more information about the incident.

"Rising gun violence is the scourge of our city, state and nation, and I support all actions to reduce it," he said.

The mass casualty shooting is the latest in the United States, where firearms are involved in approximately 40,000 deaths a year, including suicides, according to the Gun Violence Archive website.

California Governor Gavin Newsom described gun violence as a "crisis" for the United States.

"We cannot continue to let gun violence be the new normal," he said in a post on Twitter.

Lax gun laws and a constitutionally guaranteed right to bear arms have repeatedly stymied attempts to clamp down on the number of weapons in circulation, despite greater controls being favored by the majority of Americans.

Three-quarters of all homicides in the US are committed with guns, and the number of pistols, revolvers and other firearms sold continues to rise.

More than 23 million guns were sold in 2020 -- a record -- on top of 20 million in 2021, according to data compiled by website Small Arms Analytics.

That number does not include "ghost" guns, which are sold disassembled, lack serial numbers, and are highly prized in criminal circles.

In June 2021, 30 percent of American adults said they owned at least one gun, according to a Pew survey.