Thousands more people were being evacuated as some of the worst wildfires in California's history swept through wine country, leaving a trail of smoldering destruction and a death toll of at least 23.

Firefighters were locked in a fight with the wind-whipped blazes, but heading into a fourth day of the struggle, they appeared no closer to containing the fire. In fact, the fires that have burned since Sunday in Napa, Sonoma, Solano, Mendocino and Yuba counties are now threatening the towns of Sonoma, Napa, Calistoga and Fairfield.

Speaking late Wednesday, Ken Pimlott, the chief of the California Department of Forestry and Fire Protection, also known as Cal Fire, called the series of fires "a serious, critical, catastrophic event."

Pimlott gave a county-by-county breakdown of the grim toll: 13 dead in Sonoma, six in Mendocino, and two each in Napa and Yuba. Many people had to flee their homes on a moment's notice as the 30 mph winds and critically dry brush made for fast-spreading and unpredictable fires.

"We are literally looking at explosive vegetation," Pimlott said. "It is very dynamic. These fires are changing by the minute in many areas."

He said that autumn — when summer heat has dried out brush — is the most dangerous time of the year for wildfires in the state, adding that California was still feeling the effects of five years of drought.

Helicopters and air tankers were being used to hold back the shifting fire line that threatened to move on communities without warning.

Officials said 8,000 firefighters are battling large 22 fires — five more than on Tuesday. Some 170,000 acres were burning. Oregon, Nevada, Arizona and Washington state, along with the U.S. Forest Service, were sending reinforcements — crews, bulldozers and fire engines, Pimlott said. Sonoma County was getting 350 members of the National Guard to help, Sheriff Robert Giordano said.

The sheriff said he expected the death toll to go up. "The devastation is enormous," he said. "We can't even get into most areas."

Member station KQED in San Francisco reports that Cal Fire is investigating whether fallen power lines and exploding electrical transformers from an extreme wind event Sunday that saw gusts of 75 mph in Sonoma might have touched off some of the fires. Gusty winds and low humidity were possible again on Thursday.

Some 5,000 people from the historic town of Calistoga, situated in northern Napa County, were being evacuated. And in the town of Sonoma and the community of Boyes Hot Springs, officials issued an evacuation advisory.

NPR's Eric Westervelt, reporting from Calistoga, spoke with Colin Curtis, who has been eyeing with concern the rapidly moving fires.

"That fire spread so dang quick," he said. "That just shows that no one is safe anywhere around here."

The town's mayor, Chris Canning, said that given the unpredictable nature of the fires, the evacuation order for Calistoga is sensible.

"The spread of the fire and predictions on the wind, and seeing what we've seen had happen throughout our neighboring communities, obviously want to absolutely err on the side of caution here," he said.

Jessica Tunis has been calling hospitals and posting on social media in a frantic effort to find her mother, Linda Tunis, whom she last spoke to on Monday, according to The Associated Press.

All that is left of her mother's mobile home in Santa Rosa is charred ruins, the AP says.

The last thing Jessica heard her mother say was "I'm going to die" before the phone went dead.

"She's spunky, she's sweet, she loves bingo and she loves the beach, she loves her family," Jessica Tunis, crying, told the AP. "Please help me find her. I need her back. I don't want to lose my mom."

Gov. Jerry Brown has declared a state of emergency for Napa, Sonoma and Yuba counties.

"We have had big fires in the past. This is one of the biggest, most serious, and it's not over," Brown said at a news conference Wednesday, alongside the state's top emergency officials.

If the winds shifted suddenly, the fires could quickly turn, putting them on a collision course with the town of Sonoma, population 11,000.

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