At least six people were killed and 10 others wounded in a shooting in the California state capital of Sacramento early Sunday, police said.
A video posted online showed 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.
Police said no arrests had been made and the scene remained "active."
"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 around 2am in the downtown area, just blocks from the state capitol and close to the venue where the NBA's Sacramento Kings play.
The Sacramento Bee newspaper reported broken glass and police investigation markers were strewn over two blocks.
Pictures from the scene showed at least 28 such markers in a small area at the rear of an SUV.
Markers can be used by investigators to locate items of potential interest, such as shell casings.
The San Francisco Chronicle quoted a woman at the scene as saying she had been told that her husband of 12 years was among the dead.
The woman, whom the paper did not name, said a stranger had answered her husband's telephone when their daughter called, but that she had been unable to find out what had happened, despite being on police lines for several hours.
"It sounds like a lot of innocent people lost their lives tonight," the Chronicle quoted the woman saying.
"We haven't gotten an answer."
'Difficult to comprehend'
Sources told the paper that gunfire had erupted during a fracas among people coming out of bars.
Sacramento City Police Chief Kathy Lester told reporters that officers on patrol nearby had rushed to the area after hearing gunshots.
"We had a large crowd in the area. We don't know if it was part of a club or an event," she said.
Lester said six people had died and another 10 had been taken to hospital with injuries. No one was being held in custody, she said.
Community organizer Accius said eyewitnesses had told him it appeared to erupt from nowhere.
"All of a sudden folks were saying like there was issues happening on another side, folks were having an altercation and then there was gunshots and it wasn't the normal pop-pop-pop... it was some high powered artillery," he told the Sacramento Bee.
The city's mayor, Darrell 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.
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 favoured 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 per cent of American adults said they owned at least one gun, according to a Pew survey.