Updated 12 October 2017, 10:25 AEDT
Firefighters in Northern California feared resurgent winds and dry conditions will spread the wildfires that have killed at least 21 people, destroyed 3,500 homes and businesses and blanketed the state's famed wine country in smoke.
- At least 21 people killed with fears fires will spread
- More than 550 people still missing in Sonoma County
- At least 13 wineries damaged or demolished in Napa Valley
Nearly 68,797 hectares have been scorched by 22 large fires in what state fire officials say is one of the deadliest wildfire outbreaks in California history.
More than 550 people were still missing in Sonoma County, said Jennifer Laroque, a spokeswoman for the county's emergency operations centres.
It was unclear how many were fire victims or had not checked in after evacuating their homes.
Officials encouraged evacuees to let their family members know they were alright.
Santa Rosa, located in Sonoma County and the wine country's largest city, was particularly hard hit by the so-called Tubbs fire.
In some neighbourhoods, block after block was ravaged, leaving nothing but charred debris, broken walls, chimneys and the steel frames of burned-out cars.
"It's like driving through a war zone," JJ Murphy, 22, one of thousands of evacuees, said of the area around his home in the Sonoma Valley community of Glen Ellen.
Mr Murphy, five relatives, a bird, a dog and two cats piled into their camper van to flee on Monday, he said.
"It's crazy how in just a few hours a place I've recognised all my life I can't recognise," he said.
Strong winds set to challenge firefighters
Gusts of up to 80 kilometres per hour and 10 per cent humidity are forecast for parts of the Northern California fire zone.
Firefighters have worked to strengthen fire lines ahead of the anticipated increase in winds.
"The potential for new fires that could grow exponentially as these fires did in such a short time period is there," said Lynne Tolmachoff, spokeswoman for California Department of Forestry and Fire Protection, known as Cal Fire.
The weather had given firefighters a reprieve as cooler temperatures, lower winds and coastal fog let them make headway against the fires that had mostly burned in Sonoma, Napa, Lake and Mendocino counties, north of San Francisco.
At least 11 people have been killed by the Tubbs fire in Sonoma County, officials said.
It is the deadliest California wildfire since 2003, when 15 people were killed in San Diego, according to state data.
Homes burned as victims slept
Asked about the high number of fatalities, Cal Fire assistant deputy director Daniel Berlant said that some victims were asleep when the fast-moving fires broke out on Sunday night, igniting their homes before they could escape.
In Napa County, the dead included 100-year-old Charles Rippey and his 98-year-old wife Sarah, according to the county sheriff's office.
The couple were married for 75 years, a CBS affiliate in San Francisco reported, citing their son Mike.
Charles Rippey's body was found outside where his wife's bedroom once stood, Mike Rippey said.
"He was trying to get from his room to her room," he said.
"He never made it."
Wildfires have damaged or demolished at least 13 Napa Valley wineries, a trade group for winemakers there said.
But experts said smoke rather than flames may pose a greater risk to the delicate grapes still waiting to be picked.
California Governor Jerry Brown declared a state of emergency in several northern counties, as well as in Orange County in Southern California, where officials said a fire destroyed 15 structures and damaged 12.
Investigators were still determining what caused the fires, Mr Berlant said.
In some instances, winds might have toppled power poles and sparked flames, he said.