At least 13 people are dead amid mudslides in Southern California, where heavy rains triggered flooding and massive run-off, US media report.
"Waist-deep" mudslides in areas scorched by wildfires last month shut down more than 48km of the main coastal highway, officials say.
Some 163 people have been taken to hospital. Twenty had "storm-related injuries" and four were critically injured.'
More than 50 rescues have so far been performed, but a group of up to 300 people were reportedly trapped in Romero Canyon, east of Santa Barbara.
A source at the Santa Barbara Sheriff's office told the BBC the death toll was expected to climb.
The hardest hit homes were those that were not in the evacuation zone, official said.
Heavy rain run-off caused waist-deep mudflow in the Montecito, where some homes were knocked from their foundations, said Santa Barbara County Fire Department spokesman Mike Eliason.
Boulders the size of small cars were rolling down hillsides, and blocking roads, BBC Los Angeles correspondent James Cook reported.
Among those taken to safety was a 14-year-old girl who was trapped for hours in the ruins of her home.
The fire department published a picture of the girl encased in mud as she was led to safety.
County fire captain Dave Zaniboni said five people were found dead on Tuesday in Montecito and may have died as a result of the storm.
The upmarket neighbourhood includes homes owned by celebrities such as actor Rob Lowe and chat show host Ellen DeGeneres.
Oprah Winfrey also has a property in Montecito that is reportedly worth nearly $US90 million ($NZ126m).
The US Coast Guard has sent "multiple airships to support rescue operations" and warned the public not to fly drones, otherwise the flights would be forced to the ground.
Wildfires in December, including the Thomas Fire, swept through the area burning vegetation that helps prevent flooding and landslides.
Thousands of California residents were asked to evacuate on Monday for the second time in two months.
In Burbank, where waves of mud swept away vehicles, officials issued a mandatory evacuation order.
Homeowners in the area shared photos of mud in their homes.
Several roads were closed due to mudslides and debris, including the major thoroughfare Highway 101.
This is not a river. This is the 101 freeway in my neighborhood right now. Montecito needs your love and support. pic.twitter.com/jRNCBrp4b5— Ellen DeGeneres (@TheEllenShow) January 9, 2018
After a wildfire, burned vegetation and charred soil create a water repellent layer which blocks water absorption and leads to an increased risk of mudslides and floods.
"Recent burn areas would be especially vulnerable where dangerous mud and debris flows are possible," the National Weather Service said in a statement.
The Federal Emergency Management Agency shared a warning for California homeowners explaining that homes that had never flooded before were now at risk.
About 30,000 residents were under evacuation orders on Monday.
This comes after a record-setting year of $US306 billion of weather and climate-related disaster costs in the United States, the third warmest year on record, according to the US National Oceanic and Atmospheric Administration.
The storm over California is expected to produce 10 to 18cm in the foothills and 23cm in select areas.
Snow is falling at higher elevations, according to the National Weather Service.