Firefighters are continuing to tackle a huge blaze in southern California, with several of them describing it as the most ferocious they have ever seen.
An evacuation order has been issued for an area home to more than 82,000 people, just east of Los Angeles.
The Blue Cut fire, as it has been named, has destroyed homes and disrupted transport links between California and Nevada.
Some people have been running for their lives just ahead of the flames.
On Thursday morning California fire authorities assessed that the Blue Cut fire had grown overnight by almost 5,000 acres (2,025 hectares), and is only 4% contained.
The fire is continuing to grow again, as temperatures increase throughout the day.
The blaze first ignited on Tuesday in a drought-ravaged mountain pass and spread at an "explosive" pace, authorities said.
The flames have advanced, out of control, despite the efforts of over 1,500 firefighters.
Authorities are urging people to evacuate from more than 34,000 homes, but fear that up to half of them have not heeded their advice, a US Forest Service spokeswoman said.
Commander Mike Wakoski said he had never seen such extreme conditions in 40 years of service.
"There will be a lot of families that come home to nothing," said San Bernardino County Fire Chief Mark Hartwig.
"It hit hard. It hit fast. It hit with an intensity that we hadn't seen before," he added.
There are no known fatalities but dogs are searching the ruins for bodies.
Authorities have been unable to say how many homes have been destroyed, but some fear it will be in the hundreds.
At the scene - James Cook, BBC News, California
Wrightwood, a tourist resort surrounded by pine trees in the San Gabriel Mountains, feels like it is besieged by fire. Huge flames whipped by a strong breeze are advancing down a mountain ridge and along a forested valley towards the town.
Although it falls within the mandatory evacuation zone some residents have remained, keeping one eye on their homes and another on the fire.
There is no sense of panic here. The Grizzly Cafe is open and serving food to police officers and journalists.
Half of the sky is a beautiful blue but in the other direction it is ominously thick with smoke as the Blue Cut Fire rages over vast tracts of forest and desert plains.
Even for California's firefighters, experienced in tackling wildfires, this blaze - or rather series of blazes - is proving very difficult to tackle. With temperatures high and humidity low, nothing here is safe from this massive fire.
"No joke, we were literally being chased by the fire," said a tearful April Christy, sitting in a van with her mother Vi Delgado at an evacuation car park in Fontana.
Moments after first smelling the smoke, she said the flames were suddenly surrounding them.
"You've got flames on the side of you. You've got flames behind you," she said.
They grabbed their four dogs but were stopped by police from trying to rescue nine more shelter dogs and three cats, because there was no time.
Her escape involved a harrowing race down a mountain road, led by one police patrol car in front and one behind her, with firefighters battling flames alongside her.