A powerful Pacific storm has lashed southern California with wind-driven heavy rain that has downed power lines and electrocuted a man, killed a motorist in a submerged car and disrupted hundreds of flights at airports.

Homes in some central and southern parts of the state have been evacuated as a precaution due to the potential for mudslides and debris flows.

More than 300 arriving and departing flights were delayed or cancelled at Los Angeles International Airport.

In the Sherman Oaks area of Los Angeles, a falling tree downed power lines and hit a car, resulting in the electrocution of a 55-year-old man, authorities said.

Winds gusting up to 100 kilometres per hour lashed the area, and heavy rain turned creeks and rivers into brown torrents and released slews of mud from hillsides burned barren by wildfires.

Several stretches of freeways and highways were closed by flooding.

"It's crazy," said Robin Johnson, an academic adviser at the University of California, Santa Barbara.

"It's just pouring down rain. The wind is just going nuts."

In the desert town of Victorville, several cars were washed down a flooded street.

A helicopter rescued one person from the roof of a car but another motorist was found dead in a submerged vehicle, San Bernardino County fire spokesman Eric Sherwin said.

The storm took aim at southern California but also spread rain north into the San Joaquin Valley and up to San Francisco.

It was not expected to bring significant falls in the far north, where damage to spillways of the Lake Oroville dam forced evacuation of 188,000 people last weekend.

The National Weather Service said it could end up being the strongest storm to hit southern California since 1995.

The storm system was moving "very slowly" eastward and Los Angeles County was expected to see more rain through Saturday, the National Weather Service says.