A massive winter storm front swooping down on the western part of the United States has killed two people in California and caused severe flooding in northern Nevada, where more than 1,000 residents were evacuated.

The U.S. National Weather Service (NWS) Monday evening called the storm "once-in-a-decade," noting it had issued flash-flood warnings for northern and central California, western Nevada and southwest Oregon.

The NWS said the storms started over the weekend in the Pacific Northwest and would continue until mid-week, while warning more storms were on the way.

"Relentless rain and snow over much of the Western U.S. will be reinvigorated by another powerful storm moving onshore late Tuesday," the weather service said.

Mudslides crippled parts of Nevada and northern California, where a falling tree killed a woman in San Francisco and several drivers were reported trapped inside cars that were swept away.

Monday in California and Nevada, the storm caused rivers to overflow and trees to fall, triggering evacuations, power outages, school cancellations, road closures and warnings of mudslides in areas where hillsides were left barren by wildfires in the summer of last year.

Some California ski areas were closed for the second day on Monday due to avalanche concerns in the Sierra Nevada and power outages, with forecasters warning that more snow and rain were on the way.

Heavy rains and high winds were blamed for toppling a 1,000-year-old, 60-meter high, famous giant sequoia tree in California's Calaveras Big Trees State Park that featured a carved-out tunnel through the 10-meter diameter base of the tree that motorists could drive through.

Mudslides closed parts of major highways north and west of the skiing resort town of Lake Tahoe, where the NSW predicted a 4-feet (1.21-meter) snowfall by Thursday.

Dozens of roads had been cut off in the Reno-Tahoe area, where flooding forced the evacuation of hundreds of homes.

Reno, a Nevada city of 240,000 near the California border, saw at least 1,000 people evacuated Monday, and a Washoe County official said hundreds of people were expected to be housed overnight in emergency shelters.

The NWS also predicted flooding along the California coast Tuesday, as well as heavy snowfall from California to Colorado,

The heaviest snowfall was expected in the mountainous regions of Utah, Wyoming, Colorado, and especially in California's Sierra Nevada Mountains, where freezing overnight temperatures were expected to create havoc on roadways on Tuesday.

Carson, a city of 55,000 located some 50 km south of Reno, saw the Carson River overflow on Monday, as rescue crews scrambled to assess damage and clear debris.

According to the NSW, the river would crest below the 2005 flood stage, but Carson City would see sporadic weather, including rain and snow, through Wednesday.