The wind known as the Diablo is picking up again, the air is dry, there is no rain in sight and the killer fires that have scorched the wine country of Northern California remain almost completely uncontained.

Officials warned that some of the big fires could merge.

Amid these grim bulletins, the huge utility company PG&E acknowledged that the extreme winds on Monday and Tuesday had knocked trees into power lines in conditions conducive to fires. The historic wind event ... packed hurricane-strength winds in excess of [120km/h] in some cases, said Ari Vanrenen, a PG&E spokeswoman.

Vanrenen said that excess rain last winter, followed by a drought, has created a lot of dry bush.

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Officials with the California Department of Forestry and Fire Protection (Cal Fire) said they have yet to determine the cause of the fires, which have killed at least 23 people in Napa, Sonoma, Yuba and Mendocino counties.

The conflagrations have led tens of thousands of people to flee their homes. About 4400 are in shelters and will not be able to go home for many days, officials said. The Sonoma County Sheriffs Office said 560 people have been reported missing, but many may have lost cellphones or Internet access and may not have been able to reach friends or family. An additional 110 people had been located after they were reported missing.

Statewide, 8000 firefighters are working to contain 17 wildfires that cover 68,800ha - a collective area larger than the city of Chicago. The worst are in Napa, Sonoma and Mendocino counties, where 4500 homes and businesses had been burned at last count.

The fire has put a strain on federal resources, too. Coming on the heels of catastrophic hurricanes, the fires in total represent just one of 22 disasters that the Federal Emergency Management Agency is managing across the US. Eighty-five per cent of Femas 9900 full-time employees are working in the field, away from their assigned offices, agency spokesman Mike Cappannari said.

In some areas in wine country, the smoke and haze is so thick that the sun is a faint orange sphere in the sky. Most stores are sold out of air filtration masks. People pumping gas, shopping for groceries or walking dogs look like carpenters or surgeons, depending on which type of mask they were able to pick up.

Tammy Christiansen searches the remains of her Coffey Park neighborhood home. Photo / AP
Tammy Christiansen searches the remains of her Coffey Park neighborhood home. Photo / AP

Families crowd areas off the interstate highway, their cars packed with belongings.

Entire hills are scarred black. In Santa Rosa, it is possible to trace the direction of the wind by which buildings were reduced to ashes and which remained untouched.

Cal Fire Chief Ken Pimlott said a major fire in Napa County, known as the Atlas fire, was 3 per cent contained. The same modest progress had been made against the Tubbs fire, which invaded the city of Santa Rosa amid winds and immolated entire neighbourhoods.

In Santa Rosa, Ameir Kazemi stared at the smoldering remains of his business, the Mohawk Sign Company. It has been a Santa Rosa institution for 50 years, and Kazemi, 33, has owned it for a decade. Now, its a pile of ashes and charred wood.

On Tuesday, Kazemis friends began calling him at home, warning him that a fire had jumped the highway. He wanted to dash to the store, but he couldnt leave his pregnant wife. Two hours later, a local TV station broadcast video of his building on fire. It was pretty sickening, he said. I just wanted to come see if there was any chance that anything survived - the artwork, 10 years worth of stuff on my hard drive. Its all gone.

Jennifer Pierre returned to her Santa Rosa neighbourhood to see what was left of her house: almost nothing. Everything was ashes, including her childrens baby blankets that she used to spray with her perfume, her wedding dress and her wedding ring. Even the valuables in their fireproof safe had burned or melted.

She and her husband had escaped with the clothes on their backs, and the couple now smelled like the smoky remains of their home.

I could not wash that smell off me, she said.

You just want to scrub it out of you and get the smell out of you. Every time you breathe, this whole ordeal immediately comes back to you.

Christina Hanson, 27, who has spina bifida, a neural tube defect, and uses a wheelchair, was one of the people reported missing.

People salvage remains in Santa Rosa, Calif. Photo / AP
People salvage remains in Santa Rosa, Calif. Photo / AP

Her family posted the news that she did not survive the fire that struck her home on the north side of Santa Rosa.

Sonoma County Sheriff Robert Giordano said he expects the death toll to rise when officers begin going into the hot zones.

He said: We cant even get into most of the areas. When we start doing searches, I expect that number to go up.

Sheriffs office spokeswoman Misti Harris said sometimes the only way to spread crucial information is with boots on the ground.

Deputies were running toward the fire, banging on doors, getting people out of their houses, she said.

Giordano said the mandatory evacuation zones in the county remain off-limits 24 hours a day, and he doubted that residents would be able to return to their homes this week.

We are in a wickedly dangerous fire situation and when one of us needs help, all of us come, said Bob Baird, director of fire and aviation management for the Forest Services Pacific Southwest region.

Were literally looking at explosive vegetation. These fires are burning actively during the day and at night, said Pimlott.

This is a serious, critical, catastrophic event.