After years of drought and devastating wildfires, up to 35 centimeters of rain have turned large parts of California into a flood zone.
The National Weather Service warned of more flooding and mudslides in the San Francisco, Sacramento Valley and Monterey Bay area Monday after a series of winter storms hit the region in the past two weeks.
"It's just storm after storm," meteorologist Cindy Palmer told SFGate.
The mixture of unusually heavy rainfall and violent gusts of wind threatens to burden the area in the north and center of the Pacific state in the next two weeks.
Tens of thousands of Californians have already been cut off from the power supply and countless streets have been flooded.
The Santa Cruz district, about 100 kilometers south of San Francisco, meanwhile asked residents to stay at home.
Authorities have set up emergency shelters for hundreds of Californians whose homes along the coast have been flooded in recent days.
In the San Luis Obispo area, northwest of Los Angeles, a five-year-old boy was swept away by floodwaters Monday when rescuers tried to extricate him and his mother from a car.
The emergency services had to stop searching for the child after seven hours when the water continued to rise.
On Monday, the authorities also reported two more dead who had been killed by uprooted trees.
So far, 14 Californians have died in the storms.
As rain and gusts of wind also spread across southern California on Monday, authorities urged residents of Montecito to evacuate their homes.
The coastal town north of Los Angeles, which counts celebrities like Oprah Winfrey, Rob Lowe and the Ducal couple of Sussex among its residents, was hit by mudslides five years ago.
At that time, 23 people died and more than 100 houses were destroyed.
President Joe Biden meanwhile declared the disaster to support California with government funds in Washington.