Photo taken on Aug. 28, 2020 shows the wreckage at the site where a wildfire swept through in Vacaville of Solano County, Northern California, the United States. (Photo by Li Jianguo/Xinhua)

Tens of thousands of Californians were forced to flee their homes in the world-famous Napa and Sonoma wine regions Monday as another new wildfire fanned by fierce winds killed three people.

Under an opaque orange sky and a sweltering heatwave, Napa vineyards were consumed and buildings devastated by a blaze that spread at a "dangerous rate" through 11,000 acres and was zero percent contained, state fire agency Cal Fire said.

Celebrated wineries such as Chateau Boswell and part of Castello di Amorosa went up in smoke, while there was a "significant loss" of buildings on the fringes of Santa Rosa - neighboring Sonoma County's largest town - said fire chief Tony Gossner.

Around 200 miles (320 kilometers) north, three people perished in a "very fast moving, very fluid, very hot" fire in Shasta county, said Sheriff Eric Magrini.

Between the two blazes more than 35,000 residents have been ordered to evacuate, with thousands more poised to flee, as "explosive fire growth" burnt through dry vegetation and difficult mountainous terrain, officials said.

The causes of the fires are still being investigated.

Calistoga, a picturesque community at the top of the Napa Valley known for hot springs and wine, has largely been evacuated.

CeeBee Thompson spent sleepless hours watching flames in the distance and packing her car, as Calistoga's recently installed warning sirens sounded twice during the night.

"We could see flames shooting up all night long," Thompson told AFP. "The only thing we have left to do is put the cats in the car."

The inferno is threatening communities in Napa and neighboring Sonoma still reeling from devastating wildfires in 2017, when 44 people died and thousands of buildings were razed.

AFP