Updated Friday, Oct. 25, 6 p.m.

PG&E said Friday it was preparing for a "potentially historic wind event" across the state this weekend, and that as many as 850,000 customers in portions of 36 counties could have their power shut off from Saturday evening until Monday afternoon. The power shutoff could affect more than 2 million people.

The utility's warning of a similarly historic power blackout comes amid fears that very high winds, high temperatures and low humidity could spark devastating wildfires.

Shutoffs beginning on Saturday would likely affect customers in Northern and Central California. As strong winds sweep southward, shutoffs on Sunday would affect portions of PG&E's entire service area.

"We're preparing for a widespread service shutoff across our territory," PG&E Vice President Sumeet Singh said in a press briefing Friday evening, adding that the utility expects to make a decision on the shutoffs at 8:00 a.m. Saturday.

PG&E meteorologist Scott Strenfel said widespread wind gusts were expected to be 40 mph to 60 mph over most of the elevated terrain of Northern California, with peak gusts in isolated locations reaching 70 mph to 80 mph.

"Winds of this magnitude pose a higher risk of damage and sparks on the electric system and rapid wildfire spread," PG&E said. "The fire risk is even higher because vegetation on the ground has been dried out by recent wind events."

The utility also said this weekend's wind event is likely to eclipse the strength of the one that fueled the North Bay firestorm of October 2017. PG&E's predictive data models indicate the weather event could be the most powerful in California in decades.

"We do think that it will be the strongest offshore wind event this season by a large margin and if models are correct, possibly the strongest offshore winds that we've seen in years," said Strenfel. "There is high likelihood that damage will occur with this system ... this event will be a very serious event."

PG&E warned blackouts could last until Monday afternoon, but emphasized that plans could change depending on the weather forecast. Contra Costa County officials earlier said they’d confirmed with PG&E that power would go out at 10 p.m. on Saturday, and stay out through Monday afternoon.

The Alameda County Sheriff's Office also tweeted that PG&E had notified them that the county would likely experience another shutoff from Saturday at 5 p.m. until early Monday afternoon.

Alameda County sent out an AC Alert by text and email Friday that PG&E will disconnect power to approximately 57,000 residences and businesses in the county starting Saturday about 5 p.m. The alert said power is expected to be off for more than 48 hours: "We encourage you to find alternative energy sources for light, charging devices and other necessities. Plan ahead with food and water, and make sure your grab-and-go emergency kits are ready."

News of potentially more widespread and longer-lasting shutoffs came as PG&E worked to restore power to some 179,000 customers in 17 counties in the Bay Area and Sierra foothills, who’d had it turned off on Wednesday ahead of another extreme weather event.

PG&E CEO Bill Johnson said those customers would have their power restored before it is turned off again, but cautioned that might not happen in Sonoma County, where firefighters are battling the Kincade Fire that erupted Wednesday evening.

"We have about 1,000 customers in Sonoma County who remain out of service due to the Kincade Fire," a PG&E official said late Friday afternoon. "We believe we’ll be able to reduce that number to 700 customers by the end of Friday evening."

PG&E officials encourage customers who had their power shut off previously to charge all of their devices, including any necessary medical devices, before the next blackout.

PG&E said Thursday that a failure on one of its high-voltage transmission lines occurred in the area of the Kincade Fire ignition point.

The fire has forced approximately 2,000 people from their homes in Sonoma County. Its cause has not been determined.

KQED's Don Clyde contributed to this story. This story has been updated.