Californian officials warned Saturday that “extreme” wind conditions were set to fan wildfires across the north of the US state as residents were ordered to evacuate and millions faced power cuts.

About 50,000 people were ordered to flee their homes in Sonoma county, north of San Francisco, as the Kincade Fire spread to cover 25,455 acres after breaking out on Wednesday.

The blaze, which is burning in remote steep terrain, threatens 23,500 structures and had already forced the evacuation of the small community of Geyserville and nearby vineyard operations.

Hot, intense winds were forecast to pick up on Saturday and last into Monday across the San Francisco Bay area, with the affected areas put on a red flag warning indicating high risk level.

California’s largest utility, Pacific Gas & Electric Co., said it expected to cut off power to 940,000 customers — a precautionary shutdown that local media reported would affect about two million people.

“The weather event could be the most powerful in California in decades,” PG&E said, with dry northeast winds predicted to gust up to 70 miles per hour .“PG&E will need to turn off power for safety several hours before the potentially damaging winds arrive,” it added.

“Winds of this magnitude pose a higher risk of damage and sparks on the electric system and rapid wildfire spread.”About 2,000 firefighters battled the Kincade Fire, which is only 10 percent contained, according to the California Department of Forestry and Protection.