Northern California's wildfires have now killed 31 people, making this the deadliest week of wildfires in the state since records have been kept.

Recovery teams, some with cadaver dogs, will start searching for bodies in some areas devastated by wildfires raging in California wine country, while significant progress has been made in battling the blazes in the foothills of the Sierra Nevada, officials said on Thursday.

Sonoma County Sheriff Robert Giordano said officials are investigating hundreds of reports of missing people and that recovery teams will start doing targeted searches for bodies. He warns that identification may be difficult and take some time.

He said officials have found some bodies almost completely intact, while other remains are "nothing more than ash and bones."

Giordano says at least 17 people have been killed in Sonoma County. Other deaths have occurred in Mendocino, Yuba and Napa counties.

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An aerial shows damage caused by wildfires in Santa Rosa, Calif., on Oct. 11. (DroneBase/Reuters)

The wildfires already are well on their way to becoming the deadliest and most destructive in California history, but officials said Thursday some progress is being made.

Napa County Fire Chief Barry Bierman said "red flag conditions" still prevail, although winds so far Thursday were not as significant as anticipated by forecasts. 

California Department of Forestry and Fire Protection spokesman Scott McLean told Oakland television station KTVU that winds were calmer and firefighters had made some gains overnight.

Thousands of firefighters are battling at least 22 fires spanning more than 686 square kilometres for a fourth day. Some 3,500 residential and commercial buildings have been destroyed.

California Department of Forestry and Fire Protection spokeswoman Janet Upton said it's unclear if downed power lines and live wires resulted from fires or started them.

She said Thursday that investigators are looking into that and other possible causes.

Helicopters and air tankers were assisting thousands of firefighters trying to beat back the flames. Until now, the efforts have focused on "life safety" rather than extinguishing the blazes, partly because the flames were shifting with winds and targeting new communities without warning.

Giordano said over 430 are still reported missing. Officials believe many of those people will be found, however. Chaotic evacuations and poor communications over the past few days have made locating friends and family difficult.

Still, the sheriff also expects the death toll to climb.

"The devastation is enormous," he said. "We can't even get into most areas."

'It'll go up like a candle'

Smoke from the wildfires has also affected flights at multiple airports in the region.

More than 80 flights were cancelled by late Thursday morning at San Francisco International Airport, said airport spokesman Doug Yakel. Other flights taking off had been delayed an average 30 to 45 minutes, he said.

The Federal Aviation Administration said some arriving flights were delayed more than three hours.

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Napa County Sheriff deputies escort people across a barricade to be driven by police officers to pick up important medications or feed animals at their homes effected by the so-called Atlas Fire in Napa, Calif. on Thursday. (David McNew/Getty Images)

Several flights were also cancelled at Charles M. Schulz–Sonoma County Airport in Santa Rosa, a particular hotspot.

Entire cities had been evacuated in anticipation of the next wave of fires, their streets empty, the only motion coming from ashes falling like snowflakes.

They included Calistoga, the historic resort town of wine tastings and hot springs, whose 5,300 people are all under evacuation orders. Tens of thousands more were also driven from their homes by the flames. A few left behind cookies for firefighters and signs that read, "Please save our home!"

'They won't tell us nothing'

Residents in the community of Boyes Hot Springs in Sonoma County were told to clear out Wednesday, and the streets were quickly lined with cars packed with fleeing people.

"That's very bad," resident Nick Hinman said when a deputy sheriff warned him that the driving winds could shift the wildfires toward the town of Sonoma proper, where 11,000 people live. "It'll go up like a candle."

About 8,000 firefighters and other personnel were battling the blazes and more resources were pouring in from Arizona, Nevada, Washington and Oregon.

Wildfires

The California wildfires have spread in the last 24 hours, to 22 separate conflagarations. (Google)

With fires advancing from several sides in Sonoma Valley, law enforcement officers on loan from other areas of Northern California barred residents of evacuated communities from returning to see how the homes and businesses had fared. They cited the need for emergency personnel to access the areas, and dangerous conditions that included downed power lines and hydro poles that were still smouldering. 

Manned roadblocks were set up between Sonoma and devastated areas of Santa Rosa.

Alejandro Rodriguez had been evacuated from one tiny Sonoma Valley town, only to have deputies come to the neighbourhood to where he had relocated and tell residents there to pack up and go.

"I want to see my house, see if anything's left," Rodriguez said, gesturing at officers at one roadblock. "They won't tell us nothing."

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Melted metal from burnt cars is formed on the ground after wildfires ripped through the Coffey Park neighborhood of Santa Rosa on Wednesday. (Robyn Beck/AFP/Getty Images)

In Southern California, cooler weather and moist ocean air helped firefighters gain ground against a wildfire that has scorched nearly 36 square kilometres.

Orange County fire officials said the blaze was 60 per cent contained.

With files from CBC News