Heavy rain storms across large parts of California triggered floods and mudslides and left three dead as of Christmas night, local officials said.

The storms – which were expected to continue through Friday – brought 11 inches (27 cms) of rainfall to some parts of Los Angeles County, prompted evacuations and shut down major roads.

Emergency responders have had to perform several rescues, including people stuck in vehicles as flood waters rise. California's Governor Gavin Newsom declared a state of emergency on Wednesday in Los Angeles and other southern Californian counties.

About 100,000 people in the state were without power as of Thursday evening.

The US Weather Prediction Centre said on Thursday that "numerous flash flooding events are possible."

"In addition, many streams may flood, potentially affecting larger rivers."

A 64-year-old man from San Diego was killed on Wednesday morning by a fallen tree, the police department told US media.

Another person, a 74-year-old, died from flood waters over the weekend as police tried to rescue him from inside a vehicle in Redding, the town's mayor told local news.

And on Monday, a woman in her 70s died after she "was knocked off a rock by a large wave and swept into the ocean" at MacKerricher State Park in Mendocino County, the sheriff's office said.

Evacuation warnings were in effect for some residents of San Bernardino County in southern California, and flash flood warnings were issued for those in the San Francisco Bay area on Thursday morning.

Wind speeds in the Bay Area topped 100mph (161km/h) at one observatory near San Jose, the San Francisco Chronicle reported.

Reuters A house is submerged by flood waters in San Bernardino Reuters

In Altadena, near Los Angeles, flooding caused a mudlide in a vegetation-stripped area that was less able to absorb water due to the wildfires that scorched the neighbourhood in January, the BBC's US partner CBS News reported.

Los Angeles Mayor Karen Bass has also declared an emergency from the storms and warned residents to be cautious on roads during a time of busy holiday travel.

"I am urging all Angelenos to stay safe and be extremely careful on the roads if you absolutely must travel," she said in a statement on Wednesday.

"Please do not take this storm lightly."

The storms came from multiple atmospheric rivers that carried large plumes of moisture from the tropics during one of the busiest travel weeks of the year, CBS News reported. (BBC)

Update news