Severe hot and dry "devil winds" kicked up on Sunday in fire-ravaged southern California and more winds were expected in the north, fanning the flames of wildfires that have killed at least 25 people.
"This is getting bad," said Marc Chenard, a meteorologist with the National Weather Service's Weather Prediction Centre.
"We'll get sustained winds of up to 40mph [64kph] and gusts between 60mph and 70mph," he said, of the Santa Ana "devil wind" hitting the Los Angeles area.
The Woolsey Fire has been burning since Thursday in the tinder-dry canyon of Ventura County and has claimed two lives.
The air-masses blowing across the western deserts in the United States, including Death Valley, towards the coast are expected to bring the sustained high winds at least until Tuesday, Mr Chenard said.
"It's nothing but bad news."
Additional winds will blow across the Sierra Nevada foothills in northern California near Sacramento, where the so-called Camp Fire has claimed 23 lives.
The Camp Fire burned down more than 6,700 homes and businesses in Paradise, more structures than any other California wildfire on record, and the death toll, which could rise, also makes it one of the deadliest.
Only the Griffith Park Fire in 1933 and Tunnel Fire in 1991 have claimed more lives.
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Several of the bodies discovered earlier this week were found in or near burnt cars, police said. The flames descended on Paradise so fast that many people were forced to abandon their vehicles and run for their lives down the only road through the mountain town.
An additional 35 people have been reported missing and three firefighters were injured. It was not immediately clear if any of the missing were among those found dead.
As of Saturday night, the Camp Fire had charred more than 40,500 hectares at the edge of the Plumas National Forest. Crews had cut containment lines around 20 per cent of the blaze.
About 800 kilometres to the south, the Woolsey Fire burning in the foothills above Malibu doubled in size from Friday night into Sunday. The fire threatens thousands of homes and triggered mandatory evacuation orders for a quarter of a million people in city as well as other communities in Los Angeles and Ventura counties.
The fire has destroyed 177 homes and other structures, and burned through more than 33,000 hectares as of late Saturday, officials said.
"Our firefighters have been facing some extreme, tough fire conditions that they said they've never seen in their lives," said Los Angeles County fire chief Daryl Osby.
US President Donald Trump weighed in on the emergency during a trip to France and said in a Twitter post on Sunday: "With proper Forest Management, we can stop the devastation constantly going on in California. Get Smart!"
Mr Trump, a Republican, has previously blamed California officials for fires and threatened to withhold funding, saying the state should do more to remove rotten trees and other debris that fuel blazes.
State officials have blamed climate change and say many of the fires were in federally-managed lands.
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