Updated at 6:30 p.m. ET

Thousands more people were fleeing their homes as some of the worst wildfires in California's history continued to sweep through wine country, leaving a trail of smoldering destruction and a death toll that authorities say has reached 31.

Firefighters were locked in a fight with the wind-whipped blazes, but after days of struggle, they appeared to still be far from containing the flames. 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.

"We are not out of this emergency. We're not even close to being out of this emergency," Mark Ghilarducci, the director of the California Governor's Office of Emergency Services, said at a Thursday news conference.

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. State officials estimate that the fires have destroyed some 3,500 homes and other structures.

Ken Pimlott, the director of the California Department of Forestry and Fire Protection, said firefighters are battling 21 large fires after two merged. Officials said more than 8,000 firefighters are involved. More than 191,000 acres have burned.

Reinforcements — crews, bulldozers and fire engines — are coming from Oregon, Nevada, Arizona, Idaho, Montana, New Mexico, North and South Carolina and Washington state, Ghirladucci said.

Pimlott said firefighters have made progress against a set of fires known as the Wind Complex, particularly blazes in Yuba County and southwest of Grass Valley. He said they are becoming "significantly contained." This means that soon, firefighters working there can be redeployed to other areas.

Progress has also been made on the Tubbs Fire, which is burning in Sonoma and Napa counties, but it remains just 10 percent contained.

Unfortunately, weather conditions in the coming days are not expected to make the firefighters' job any easier. "Over much of the state, we'll have critical dry humidity and windy conditions throughout the weekend," Pimlott said. "This means our fires are going to continue to burn erratically. They have the potential to shift in any direction at any time."

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

He said that autumn — when summer heat has dried out the 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.

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

Giordano told reporters that officials had received 1,000 reports of missing persons in the county, though many appear to be duplicates and hundreds were later found safe. He said Thursday that around 400 people were still missing.

"We're moving into a recovery phase," he said. Detectives are investigating the missing persons reports, sending teams and trained dogs to search homes when the area is safe to enter. "We're doing targeted searches," he said, stressing that this process will be slow.

The sheriff added: "Identification is going to be hard," because not all recovered bodies are intact.

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.