Mudslides, flooding and strong winds are battering southern California as a second day of storms drenches one of the most populous parts of the US.
Heavy rain of up to 1in (2.54cm) an hour could hit areas around Los Angeles for at least 24 hours from Monday.
The “atmospheric rivers” causing the storms have already seen swathes of the state hit by rain, wind and snow.
The storm killed one man in Sacramento Valley, who died after a tree fell on him due to fierce winds.
A state of emergency has been declared in 10 of the state’s counties.
Forecasters have said torrential rain is the main risk facing California on Monday.
The Weather Prediction Service (WPC), part of the National Weather Service (NWS), issued a level 4 warning for rainfall in parts of southern California.
The WPC said potentially “life-threatening” and “catastrophic” flash flooding threatened the Los Angeles Basin and surrounding area. It said mudslides and debris flows were also a risk.
The centre added that “very heavy” snows would continue in the Sierra Nevada mountains, rendering travel “dangerous to impossible”.
The NWS said strong winds of up to 70mph (112kmph) could cause further power cuts and downed trees, though winds would decrease significantly by Monday night.
Large steep waves would make areas along the coastline “extremely dangerous,” it added.
On Sunday, flights from Santa Barbara Airport were cancelled and drivers stranded by flooding in Los Angeles had to be released by rescuers.
More than half a million people were without power on Monday morning as the storm knocked out electricity networks.
Evacuation orders were issued for residents in several counties, including Los Angeles, Santa Clara and Santa Barbara.
The storm is due to an “atmospheric river” effect, caused by airborne currents of dense moisture.
Atmospheric rivers are a phenomenon in which water evaporates into the air and is carried along by the wind, forming long currents that flow in the sky like rivers flow on land.
A first atmospheric river hit California last week. The renewed bout of bad weather is caused by a second.
In a statement declaring the state of emergency in eight counties, including Los Angeles and Orange, Governor Gavin Newsom said: “This is a serious storm with dangerous and potentially life-threatening impacts.
“California is ready with a record number of emergency assets on the ground to respond to the impacts of this storm.
“Two other counties have declared their own states of emergency.
The NWS said Monday would be “one of the most dramatic weather days in recent memory”.
NWS officials urged people in affected areas to heed evacuation orders, stay off the roads and be prepared for potential power cuts.
