At least 13 people are dead amid "waist-deep" mudslides in Southern California, where heavy rains triggered flooding, say officials.
Some 163 people have been taken to hospital. Twenty had "storm-related injuries" and four were critically hurt.
A group of up to 300 people are reportedly trapped in Romero Canyon, east of Santa Barbara.
Police said the scene "looked like a World War One battlefield".
The flooding and mudslides, affecting areas scorched by wildfires last month, have shut down more than 30 miles (48km) of the main coastal road.
Emergency services said a number of people were unaccounted for and they expected the number of deaths to rise.
Thousands fled the deluge and more than 50 rescues have been performed.
The hardest-hit homes were those that were not in the evacuation zone, officials say.
Heavy rain run-off caused a mudflow in the community of Montecito, where some homes were knocked off their foundations, said Santa Barbara County Fire Department spokesman Mike Eliason.
Boulders the size of small cars were rolling down hillsides and blocking roads, reports BBC News Los Angeles correspondent James Cook.
Among those taken to safety was a 14-year-old girl who had been 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.
View from the air in Montecito. Areas that had been roadways, driveways, and homes, are now unrecognizable due to the large amount of mud and debris flows. pic.twitter.com/dbsUPw3mrL— VenturaCoAirUnit (@VCAirUnit) January 9, 2018
County Fire Captain Dave Zaniboni said that five people were found dead on Tuesday in Montecito and may have been killed as 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 $90m (£66m).
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
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 grounded.
Thousands of California residents were asked to leave their homes on Monday for the second time in two months.
In Burbank, where waves of mud swept away vehicles, officials issued a mandatory evacuation order.
Please see photos from the storm. If you witness significant mud, debris or fast flowing water, do not try to cross, or drive a vehicle through it and shelter in place. pic.twitter.com/RQNTHPc5z6— City of Burbank (@BurbankCA) January 9, 2018
Homeowners in the area shared photos of mud in their homes.
Several roads are closed, including the major Highway 101.
Wildfires in December, including the Thomas Fire, swept through the area burning vegetation that helps prevent flooding and landslides.
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 will be especially vulnerable where dangerous mud and debris flows are possible," said the National Weather Service 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.
This comes after a record-setting year of $306bn (£226bn) 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 4in to 7in (10 to 18 cm) in the foothills and 9in (23cm) in select areas.
Snow is falling at higher elevations, according to the National Weather Service.
Flash flood / massive amounts of mud swept thru #montecito oaks neighborhood. Mud buckling doors trying to get in house. People on roofs. Power out. Power lines down all over #mudslide pic.twitter.com/1SvgOpqBTw— Benjamin Hyatt (@caffeineben) January 9, 2018
Did You Know?— FEMA Region 9 (@femaregion9) January 8, 2018
Homes near burned areas can flood, even if they never have before. Regular homeowner's insurance does not protect against flood damage.
There is a 30-day waiting period before most flood insurance policies are effective. pic.twitter.com/YV62ehGpNA