A swiftly spreading wildfire destroyed hundreds of homes and forced thousands of residents to flee as it roared unchecked through the northern California village of Middletown and nearby communities, fire officials said on Sunday.
The so-called Valley Fire, now ranked as the most destructive among scores of blazes that have ravaged the drought-stricken Western United States this summer, came amid what California fire officials described as "unheard of fire behaviour" this season.
A separate fire raging since Wednesday in the western Sierras has leveled more than 130 buildings and was threatening about 6,400 other structures, with thousands of residents under evacuation orders there, too, the California Department of Forestry and Fire Protection (Cal Fire) reported.
Governor Jerry Brown declared a state of emergency in both areas, and mandatory evacuations were expanded as shifting winds sent flames and ash from the Valley Fire toward a cluster of towns in the hills north of Napa Valley wine country.
Reuters video footage from Middletown showed a smoking, devastated landscape of blackened, burned-out vehicles and the charred foundations of buildings that had been reduced to ash.
"While crews have not had a chance to do a full damage assessment ... we know hundreds of structures have been destroyed," Cal Fire spokesman Daniel Berlant said in a Twitter post.
Property losses included "countless homes and other buildings," he added in a subsequent video news briefing.
The Valley Fire has consumed more than 50,000 acres (20,200 hectares) since igniting Saturday in rural Lake County, California, about 50 miles (80 kms) west of Sacramento, the state capital, fire officials said on Sunday.
Thousands of evacuees from Middletown, Cobb, Hidden Valley Lake and the Harbin Hot Springs resort gathered in shelters, restaurants and friends' houses in nearby Kelseyville and Calistoga to await word on their homes, horses and dogs.
The mountain town of Cobb was hit first Saturday afternoon, and the blaze reached Middletown before sunset a few hours later, Cal Fire spokeswoman Amy Head told Reuters. The two communities, each with a population of roughly 1,500, were among the areas that bore the brunt of the flames.
A combination of drought and a heat wave last week had left vegetation tinder dry and highly combustible, setting the stage for a conflagration that thwarted the best efforts of firefighters to contain it, Berlant said.
"Every time they made progress, the fire would burn right past them," he said, adding that embers carried by the wind were sparking new blazes and enlarging the fire zone.
During its first 12 hours, the blaze had devoured 40,000 acres of forest, brush and grasslands at what Head called an "unprecedented rate" of spread for a wildfire.
Four firefighters were hospitalised with second-degree burns in the early hours of the blaze and were listed in stable condition on Sunday, but no other casualties were reported, Head said. Thick smoke later kept water-dropping helicopters and airplane tankers grounded, she said.
'FLAMES ALL AROUND'
Laura Streblow, 27, an evacuee who fled Hidden Valley Lake with her boyfriend on Saturday night and was tracking developments on social media and through friends, told Reuters she had heard that "Middletown is basically gone."
"I saw flames all around ... The wind was insane. I have never been so scared," she said.
Mark Donpineo, 54, said he and two friends were trapped by the fire for four hours Saturday evening at a golf course in Hidden Valley Lake, taking cover in a culvert until the flames had passed.
"We got some towels, wetted them down and basically saw the fire coming. You could hear explosions of propane tanks, the ridge was totally on fire, trees were blowing up," he said.
Meanwhile, Cal Fire reported that 81 homes and 51 outbuildings had been lost in the four-day-old Butte Fire, which has charred more than 65,000 acres in the mountains east of Sacramento but was 20 per cent contained.
As of Sunday, firefighters were battling nearly three dozen large blazes or clusters of fires in California and six other Western states, according to the National Interagency Fire Center in Boise, Idaho.