A man fatally shot 10 people and injured at least 10 others at a ballroom dance hall during a Chinese Lunar New Year celebration late on Saturday near Los Angeles before fleeing the scene, police said.

The shooter, still at large 12 hours after the attack in the city of Monterey Park, was believed to be an Asian man between 30 and 50 years old based on descriptions from eyewitnesses, law enforcement officials said.

"We need to get this person off the street as soon as possible," Los Angeles County Sheriff Robert Luna told reporters at a Sunday morning news conference in Monterey Park, home to one of the largest Asian American communities in the United States.

Earlier on Sunday morning, the sheriff's department said it did not know whether the attack was racially motivated. Five of the victims were male and five were female, Luna said. Their identities have not been made public.

Officials were investigating whether an incident at another dance venue in the neighbouring city of Alhambra about 20 minutes later on Saturday night was connected with the massacre in Monterey Park. At the second venue, witnesses said an Asian man walked in holding a gun that patrons were able to grab. No one was shot and the man fled, Luna said.

When police arrived at the Monterey Park ballroom, people were "pouring out of the location screaming," department captain Andrew Meyer told reporters at a news briefing.

At least 10 people were taken to local hospitals to be treated for injuries and at least one was in critical condition. Police have not said what kind of gun was used in the attack.

The shooting took place after 10pm local time around the location of a two-day Chinese Lunar New Year celebration where many downtown streets are closed for festivities that draw thousands of people from across Southern California. Police said the celebrations planned for Sunday were cancelled.

Residents stood gazing at the many blocks sealed off with police tape on Sunday in Monterey Park. Chester Chong, chairman of the Chinese Chamber of Commerce of Los Angeles, described the city of about 60,000 people as a quiet, peaceful, beautiful place where everybody knows each other and helps each other.

About 11 kilometres from downtown Los Angeles, the city has for decades been a destination for immigrants from China. Around 65 percent of its residents are Asian, according to US Census data, and the city is known for its many Chinese restaurants and groceries.

"People were calling me last night, they were scared this was a hate crime," Chong said at the scene. (Reuters)