SONOMA, Calif. (Reuters) – Firefighters struggled to halt the spread of wildfires that have killed at least 23 people in Northern California and dry, gusty winds threatened on Thursday to push flames into the evacuated town of Calistoga.

Nearly two dozen fires spanning eight counties have raged largely unchecked since igniting on Sunday, leaving hundreds of residents unaccounted for.

The National Weather Service warned on Thursday morning of persistent “critical fire weather conditions” in the area for the next three days, with no rain expected and dry winds from the north with gusts upward of 35 miles per hour (55 kph).

The deadliest of California’s blazes, known as the Tubbs fire, was within 2 miles (3 km) of Calistoga, a community in the world-renowned Napa Valley wine country whose 5,000 residents were told to leave their homes on Wednesday.

Whether the town burns “is going to depend on the wind,” Calistoga’s Fire Chief Steve Campbell told Reuters early on Thursday. “High winds are predicted but we have not received them yet.”

New evacuations also were issued in Sonoma County late on Wednesday for parts of Santa Rosa, the largest city in the wine-producing region, and Geyserville, an unincorporated town of 800 people.

The fires already have charred about 170,000 acres (69,000 hectares) of land and destroyed some 3,500 buildings. Neighborhoods have been reduced to panoramas of ash, charred trees and burned-out cars.

While their cause has not been determined, the blazes are thought to have been sparked by power lines toppled by gale-force winds and fanned by arid winds that blew into Northern California toward the Pacific.

Wildfires have damaged or demolished at least 13 Napa Valley wineries, a vintners’ trade group said on Tuesday.

About 25,000 people remained displaced on Wednesday as the fires belched smoke that drifted south over the San Francisco Bay area, where some residents donned face masks.

More than 285 people still were missing in Sonoma County late on Wednesday night, the sheriff said on Twitter. It was unclear how many might be fire victims rather than evacuees who had not checked in with authorities.

The 23 recorded deaths make the fires the deadliest in the state since 1991. The Tubbs fire, which has accounted for 13 of the deaths, is the worst single blaze since 2003, according to state data.

In addition to high winds, the fires have been stoked by an abundance of thick brush left ready to burn by a dry, hot summer.

California Governor Jerry Brown has declared a state of emergency in several northern counties, as well as in Orange County in Southern California, where a fire in Anaheim destroyed 15 structures and damaged 12.