AT least eight people were shot on Sunday night at an apartment complex in San Bernardino, California - with at least two of the victims reportedly in "extremely critical" condition.

Police originally said 10 people were shot and three were in critical condition, but the numbers were updated on Monday morning, reports Fox News.

Police said the youngest person shot was 17-years-old and in "extremely critical condition," NBC Los Angeles reported.

"We got a call about 10.45pm (2.45pm AEST) for shots fired," said San Bernardino spokesman Captain Richard Lawhead.

"We found [eight] victims down at the scene. Three are extremely critical."

The shooting happened on a hot holiday weekend in the city that is about 96km east of Los Angeles.

Police have set up a large perimeter around the crime scene, according to KTVN-TV in Los Angeles.

Multiple handguns and rifles were fired by gunmen who fled the scene, according to Capt. Richard Lawhead of the San Bernardino Police Department.

Police arrived at the location on Sunday night to find an "unruly crowd" at a common area in the apartment complex of about 100 units, Captain Lawhead said.

It appeared the crowd of people may have been playing a game of dice when the shooting occurred, the Press-Enterprise reported.

"It was a chaotic scene," Captain Lawhead said.

A woman who lives near the complex told CNN that she heard 15 to 20 gunshots fired in quick succession.

"My brother-in-law could hear bullets flying past our house. He was outside at the time of the shooting," the woman said.

"About five minutes later, the helicopter was circling around our street, talking on the loudspeaker saying to put down the weapons, for the people who were on the ground to get up and get to safety and to let the law enforcement do their job."

Another neighbour reportedly told the network, "I heard around four shots, then what sounded like a motorcycle speeding off. After that, just a continuation of gun shots."

So far no arrests have been made and there was no immediate description given for any suspects.

Captain Lawhead said there was gang activity in the area but it was not immediately clear if that was connected to the shooting.

Prominent California Democratic senator Kamala Harris tweeted about the shooting, sending her thoughts to those affected, saying she was "heartbroken" over the shooting.

Captain Lawhead said that as of early Monday morning, detectives did not have a suspect or a motive in the shooting. No weapons were recovered at the scene, he said.

The shooting took place a week after a gunman shot nine people and killed two competitors at a video game tournament in Jacksonville, Florida. - with Fox News