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, prompting 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 Center said on Thursday that numerous flash flooding events are possible.

A 64-year-old man from San Diego was killed on Wednesday morning by a fallen tree, and 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.

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.

Evacuation warnings were in effect for some residents of San Bernardino County, 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.

In Altadena, near Los Angeles, flooding caused a mudslide in a vegetation-stripped area that was less able to absorb water due to recent wildfires.

Los Angeles Mayor Karen Bass has also declared an emergency, warning residents to exercise caution on the roads during this busy holiday travel period.

These storms were fueled by multiple atmospheric rivers carrying moisture from the tropics, hitting California during one of the busiest travel weeks of the year.