Fanned by warm, dry winds, the fires have grown so big, so fast, that the immediate goal fire officials set was not so much to stop the spread as to slow it, to channel it away from threatened cities and towns, and to save lives. Saving homes and businesses was secondary.

The fires have killed at least 29 people in Northern California, officials said on Thursday. Fifteen of the deaths were in Sonoma County. Officials cautioned that the figures could rise as emergency workers are able to return to scorched areas and search for hundreds of people who have been reported missing.

Robert Giordano, the Sonoma County sheriff, said, “So far, in the recoveries, we have found bodies that were almost completely intact, and we have found bodies that were nothing more than ash and bones.” In some cases, he said, the only way to identify the victims was by the serial numbers stamped on artificial joints and other medical devices that were in their bodies.

Statewide, there were 21 major fires burning on Thursday, having consumed more than 191,000 acres since the outbreak began on Sunday night, said Ken Pimlott, the chief of Cal Fire, the state firefighting agency. The number of separate fires rises and falls often, as new blazes flare up and old ones merge with one another, but the size of the devastated area has grown steadily.

In the hardest-hit region, in Napa and Sonoma Counties, the sun was an orange dot in a leaden haze. There were eight major blazes there on Thursday, and the burned area grew to more than 120,000 acres, Cal Fire reported. The agency said that the 34,000-acre Tubbs Fire, which has burned parts of the city of Santa Rosa and has threatened Geyserville, was 10 percent contained, but most of the other blazes in wine country were 3 percent contained or less.

Officials threw out sobering figures on the scale of the devastation, with the caveat that the numbers were just estimates, sure to rise when the crisis has abated enough to allow an accurate damage assessment. Thousands of structures have been destroyed, many more are threatened, and tens of thousands of people have been displaced.