Northern California officials ordered a new round of mandatory evacuations for parts of the Sonoma Valley and eastern Santa Rosa as gusting winds returned, reviving dangerous fire conditions in a region that has been devastated by ongoing blazes.

The National Weather Service warned that strong winds were expected throughout Northern California, with gusts of 55 to 70km/h, putting much of the region under a red flag warning. "If any new fires start, they could spread extremely rapidly," the NWS said. Dangerous winds and extremely dry "fuels" on the ground "also could cause problems with the current wildfires and the firefighters trying to suppress them," the NWS noted.

"If you live in the areas below, LEAVE NOW!" Sonoma County officials wrote. The evacuation order affected thousands of residents, as the Nuns fire remained a "big, unwieldy beast," a fire spokesman told KQED News. In neighbouring Napa County, to the east, officials said that they did not expect any new evacuations but cautioned its residents to remain vigilant because of "significant wind activity".

Even as several fires still burn across hundreds of hectares in California wine country, the horrific scale of death and destruction is coming into focus.

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At least 37 people have been confirmed dead in four counties, many of them elderly, some burned to ashes. One victim was 14 years old. Taken together, the disastrous blazes - more than 20 in all, including at least six in Sonoma County - have killed more people than any other California wildfire on record. The death toll is certain to rise as authorities - some with cadaver dogs - continue to explore the wreckage.

An aerial view shows the devastation of the Coffey Park neighborhood after a wildfire swept through. Photo / AP
An aerial view shows the devastation of the Coffey Park neighborhood after a wildfire swept through. Photo / AP

Hundreds are still missing. Statewide, an estimated 5700 structures have been destroyed, including whole neighbourhoods reduced to smoldering rubble. About 90,000 people have been displaced.

"It's devastating. I've only driven maybe 5 per cent of the fire area... I don't even think I understand what the damage toll is going to be, and I have a better handle on it than most," Sonoma County Sheriff Rob Giordano told the Los Angeles Times. "Santa Rosa will be a different planet. There is so much to rebuild. It will absolutely change the community."