Hundreds of rescuers are combing wreckage in Southern California for more than a dozen people missing after mudslides that have killed 17 people.
Another 28 injuries have been reported in Santa Barbara County following the deluge that overwhelmed an area scorched by wildfires last month.
More than 100 homes were destroyed, and another 300 have been damaged. Santa Barbara County Sheriff Bill Brown said 13 people remain missing.
The death toll rose on Wednesday afternoon after two more bodies were found, he added. More than 50 people have been rescued already but many places were still inaccessible.
Several roads were closed, including the major Highway 101 which authorities say will not be reopened until Monday. "We are still very much in active search-and-rescue mode," said Chris Elms, a spokesman for Cal Fire, cautioning that the death toll may still rise.
"That's a fear. We are still very hopeful that we will locate people alive," he added.
Santa Barbara County spokesman Amber Anderson said: "We have no idea where they're at. We think somewhere in the debris field".
The first rain in months caused mudslides when it hit ground that had been burned by December's huge wildfires.
After a wildfire, burned vegetation and charred soil create a water repellent layer which blocks water absorption.
Together with the loss of vegetation, this leads to an increased risk of mudslides and floods.
The Federal Emergency Management Agency says the risk of flooding stays "significantly higher" for up to five years after a wildfire.
"Recent burn areas will be especially vulnerable where dangerous mud and debris flows are possible," said the National Weather Service in a statement.
In some places mud was waist-deep, officials said. Thousands had to leave their homes, many for the second time in two months. The emergency services declared an exclusion zone, saying anyone moving around the area would be in the way of rescuers and would be subject to arrest.
Those who have stayed in the area have been warned to boil their tap water before drinking it. 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.
County Fire Captain Dave Zaniboni said five people were found dead on Tuesday in Montecito, possibly as a result of the storm.
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.
This comes after a record-setting year of $306bn (£226bn) of weather and climate-related disaster costs in the United States, with 2017 the third warmest year on record, according to the US National Oceanic and Atmospheric Administration. California has suffered severe drought in five out of six of the past years.
In December, California Governor Jerry Brown said the state was "facing a new reality" as climate change meant wildfires could erupt "every year or every few years".
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