Santa Rosa, Calif. — A series of historically deadly Northern California wildfires regained momentum Wednesday as winds whipped back up, pushing blazes through parched hills and vineyards and prompting more evacuations from an arc of flames that has killed at least 17 people, destroyed more than 2,000 buildings and battered the region's renowned wine-growing industry.

Officials ordered a fresh round of mandatory evacuations in flame-battered Sonoma County, where one of the blazes, known as the Tubbs Fire, has killed 11 people. The massive fire, one of several that has been ravaging the region since Sunday, advanced overnight toward populated areas, prompting the additional evacuations, Sonoma County Deputy Sheriff Brandon Jones said.

Higher winds could hamper efforts to contain the fires over the next few days, fire officials said.

Tubbs is already California's deadliest wildfire since 2003, when 15 people were killed in the Cedar Fire in San Diego County. With more than 180 people still reported missing in Sonoma County, authorities expect the death toll to rise.

"This has been one of the deadliest weeks for fires that we've experienced in recent time," Daniel Berlant, assistant deputy director for Cal Fire, said Wednesday. "And a lot of that has to do with the fact that the fires ignited overnight. Many people were asleep when the fire started. Getting them evacuated was an extreme challenge for rescue crews."

The two biggest wine-country fires, Tubbs and one known as Atlas that began in Napa County, grew overnight as conditions worsened and had torched a combined 54,000 acres by Wednesday morning, according to Cal Fire.

The fast-moving flames have swept through densely populated neighborhoods over the past two days, causing residents to flee from homes in the middle of the night as smoke filled their rooms. One couple had to jump into their pool as flames rushed across their land, taking occasional gasps for air as flames lapped at their backs.

High winds that whipped up 17 large fires had faded earlier Tuesday and humidity increased, assisting an operation that has drawn resources from throughout the state and neighboring Nevada. But officials warned that the sharp northern wind, known as a Diablo, would return, allowing only a brief window for firefighters to carve clearings in place to stop the fires from spreading to vulnerable populated areas.

That wind returned Tuesday night, along with lower humidity levels.

The National Weather Service expects these "red-flag" conditions — including wind gusts up to 40 mph — to remain until Thursday in the North Bay Area, which includes Sonoma and Napa counties.

On Wednesday morning, as weary firefighters attempted to control the fires on the front lines, dozens of fire crews from cities as far away as Bakersfield, more than 300 miles to the south, were briefed on the deteriorating conditions at a command center set up at the Sonoma County Fairgrounds.

More than 25,000 people have fled homes from seven counties north of San Francisco, filling dozens of shelters that state officials had hoped to consolidate in the coming days to provide more-efficient services. Many left houses with nothing, and officials acknowledged Tuesday that it could be weeks before some are able to return to what is left.

"These fires came down into neighborhoods before anyone knew there was a fire in many cases," Cal Fire Chief Ken Pimlott said during an afternoon news conference. "This is just pure devastation and it's going to take us a while to get out and comb through all of this."

The scope of the damage prompted President Donald Trump on Tuesday to approve federal emergency assistance to California, agreeing to a request made by Gov. Jerry Brown, D. The declaration, announced by Vice President Mike Pence during a visit to the state's Office of Emergency Services near Sacramento, provides immediate funds for debris clearing and supplies for evacuation centers, among other aid.

"I appreciate the fast response from the president," Brown said in a brief statement.

The fires are the most destructive in what already has been a severe wildfire season for California and much of the West, where more than 8 million acres have been charred this year. In his letter to Trump, Brown said that nearly 7,500 fires have flared in California this year. Ten of them have prompted him to declare a state of emergency.

As a thick haze coated the sky and settled into the region's canyons and valleys, state officials remained focused on rescue and containment.

The cause of the fires, which flared overnight Sunday and blew swiftly through more than 120,000 acres in the following days, was unknown and likely to remain so for some time.

Pimlott said the possibility that a lightning strike started the fires was "minimal." In California, he said, 95 percent of wildfires are started by people, inadvertently or intentionally. "All of these fires remain under investigation," he said.

State officials said that firefighters planned to clear lines between the Atlas Fire and the city of Napa, and between the Tubbs Fire and the city of Santa Rosa — the largest in Sonoma County and gateway to the wine-tourism industry.

Those barriers would protect the areas from the south with the expectation that winds will shift back to the north in the days ahead.

Officials said the idea, in the case of the Tubbs Fire, was to prevent a "reburn" of Santa Rosa.

For Dylan Sayge, the original burn was devastating. He and his roommates were awake early Monday morning when they noticed an unusual sight outside their $1,600-a-month rental home in the Coffey Park neighborhood of Santa Rosa.

"We realized ash was falling from the sky," said Sayge, 23, a musician who works at Trader Joe's.

Soon after, online, they learned that a fast-moving fire had jumped Highway 101, propelled by howling winds. The power flickered and an explosion followed as a transformer blew nearby. They grabbed their three dogs — Cash, Willie and Shorty — and their cat, Apollo. Sayge packed up baby pictures and musical instruments.

They headed out in three cars and into a traffic jam. Sayge left behind a 1998 Ford Taurus that he had just been given as a gift. The dense smoke clouded visibility. He eventually made it to a friend's home in Fairfax, down the road in Marin County.

The next day, he learned that the house was gone, the Taurus a charred husk.

"The world can change in any moment," Sayge said. "Anytime."

Kerr reported from Healdsburg, Calif; Donosky from Windsor, Calif.; and Phillips and Wilson from Washington. Alissa Greenberg in Berkeley, Calif., and Kimberly Kindy, Joel Achenbach, Herman Wong and Amy B Wang in Washington contributed to this report.