Drone video taken over part of Santa Rosa, California Tuesday shows residential areas scorched by the inferno that swept through the area late Sunday into Monday. Officials say wildfires destroyed as many as 2,000 homes and businesses. (Oct. 10)

SONOMA, Calif. — The death toll rose to 21 Wednesday and more than 3,500 homes and businesses have been destroyed across Northern California’s wine country as almost two dozen wildfires continued their assault on the region for a fourth day Wednesday.

The California Department of Forestry and Fire Protection said fire activity increased significantly, destroying more buildings and forcing more mandatory evacuations. The wind-whipped, fast moving cluster of blazes ranks among the most destructive fire events in U.S. history. 

“This is a serious, critical, catastrophic event,” Cal Fire Chief Ken Pimlott said. “It’s pure devastation, and it’s going to take a while to get out and comb through all this.”

Air rescue teams have plucked more than 50 people from roofs and mountaintops. Chris Childs, with the California Highway Patrol, said pets have been included in the rescues. He also cautioned that all evacuees must remain patient before returning to their homes.

“I know it’s a tough message to be told you cannot go back to your homes, but I ask for your patience as you deal with officers at those road closures,” Childs said.

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More than 250 square miles have burned since the fires began igniting Sunday. Authorities have yet to determine the cause of the fires, but they say the weather has complicated efforts to fight them.

“Yesterday was a very aggressive day for fire expansion,” Cal Fire’s deputy commander Barry Biermann said. “We had a lot of wind.”

The toll has been brutal: At least 21 dead, thousands of homes, businesses and other buildings destroyed. Sonoma and Napa counties have taken the brunt of the damage.

Sonoma County Sheriff Rob Giordano said 11 deaths have been confirmed in his county alone.

“When we start doing searches, I would expect that number to go up,” Giordano said.”The devastation is enormous.”

Giordano said more than 600 missing persons reports have been filed. He said the vast majority were due to cellphone issues, including spotty service and drained phone batteries as residents packed and fled in a hurry. As of late Wednesday, the sheriff’s office said 315 of the missing persons have been located safely.

He urged people in evacuation zones to leave sooner, not later.

“People underestimate how powerful this can be,” Giordana said.

Dean Knight fled his home in the mountains of Glen Ellen for a familiar shelter at Sonoma Valley High School. Knight taught chemistry at the school for 46 years. Since Sunday he has been passing out water and facemasks and otherwise helping out in any way he can.

He also can lend an empathetic ear to some of his 250 fellow evacuees. Some talk of losing everything. All he knows about his own home is that neighbors said it was still standing Monday.

“Whatever happens, happens,” he said. “The main thing is people got out. … We’re keeping our fingers crossed.”

Vivian and David Stanley fled to the shelter Sunday, grabbing some clothes, blankets, pictures and a safe after a neighbor banged on the door, warning them to leave.

“Neighbor to neighbor, they didn’t want anyone left behind,” Vivian Stanley said.

Fog and relatively cool temperatures descended on the hard-hit area Wednesday, but the National Weather Service had little good news for the 4,000-plus firefighters battling the blazes for a fourth day.

“No rainfall is forecast for ongoing fires in California,” the weather service said. “Strong winds behind the front will bring elevated-to-critical fire weather threats to active fires across northern California today into Thursday.”

Residents are in a state of uncertainty, wondering about their homes and, in some cases, the welfare of their relatives or neighbors. Police set up a voluntary evacuation order for the gated community of 150 homes at Eastridge in Green Valley, Calif. just north of Fairfield.

Multiple police and fire vehicles have staged at the entrance of the community, carefully watching a fire that’s been burning in the hills to the north since Tuesday night.

Out in front, nearby neighbors come in a steady stream to ask anxious questions.

“We are next,” said Francisco Moreno, who lives in the Vintage neighborhood just down the street.

“We’ve got everything packed and ready to go as soon as they tell us to,” he said.

About a mile up Green Valley Road by a country club, the scene is tranquil. Fire trucks are parked at the side of the road along with multiple media trucks and police vehicles. All are here should the fire in the hills above suddenly spring into movement with the higher winds that are expected as evening comes.

Neighbors who haven’t evacuated water their roofs and lawns as delicate white ash rains down upon the area.

Marcella Warfield lives in upper Green Valley and has been under mandatory evacuation since Monday. “I got out with two pairs of jeans, some mementos and my great Dane. I’m still trying to get someone to go back and get my new car. They’re just weren’t enough of us to drive out when word came we needed to leave.”

She said as far as she knows, her house, which is 4,000 feet from the edge of the fire, is still standing.

“What if the winds really pick up tonight, I don’t know.I just got to be ready to lose everything. “

Contributing: Elizabeth Weise; The Associated Press