(CNN) Nearly a million homes and businesses in California were slowly going dark Saturday as the state's largest utility shut off power in an attempt to avoid "catastrophic" wildfires.

The power was turned off in phases through Saturday night and will begin to be restored Monday, the utility said.

Hurricane-force winds with gusts up to 90 mph could hit the state Saturday night into Sunday, adding to the already fire-prone conditions in the state.

The utility feared the strong winds would knock down trees or debris, affecting its power lines and poles.

"When debris hits these wires, any spark could be an ignition source of a catastrophic wildfire," said PG&E CEO and president Andy Vesey.

More than seven million people were under red flag warnings Saturday across the Sacramento Valley, with critical to extreme fire dangers over the coming days.

"The level of winds, gusting to almost 90 mph presents a real threat and an opportunity for wildfires and we are not going to let that happen," Vesey said.

High wind warnings and advisories were in place across much of northern California as winds increased and peaked Saturday evening and overnight, according to CNN meteorologists.

Scott Strenfel, a PG&E meteorologist, said the wind event could be one of the strongest in the last several years and likely one of the longest.

San Jose 'power vulnerability plan' months in the making, officials say

PG&E has been under scrutiny in recent years for the role its equipment played in several devastating fires across the state, including last year's deadly Camp Fire . Over the last weeks, the utility has been enacting preventative shutoffs all over northern and central California, but this weekend's could be the largest this year.

The 36 counties losing power, the utility said, include Humboldt, the Sierra foothills, Western Sacramento Valley and the greater Bay Area. Paradise, which was devastated by last year's deadly Camp Fire, is also among the areas to be left in the dark.

In San Jose, City Manager Kip Harkness told reporters the city has a plan in place for the outage.

The outage could affect as many as 90,000 people in the San Jose area but "we expect it to be a little lower than that," Harkness said.

If power remains off into Monday, Harkness said, individual school districts will determine whether to close schools.

"Take care of yourself and your family and then, if you're OK, take a little moment across the hall, across the street and check in on your neighbor," he said. "See how's she's doing, make sure she has what she needs to make sure she's safe.

San Jose officials said the city has activated a "power vulnerability plan" that was months in the works.

PG&E said the utility would start by shutting off power at 2 p.m. (local time) Saturday in parts of rthe counties of Amador, Butte, Colusa, El Dorado, Glenn, Nevada, Placer, Plumas, San Joaquin, Sierra, Siskiyou, Shasta, Tehama and Yuba.

The outages will be staggered, with the sixth and final phase beginning at 10 a.m. (local time) Sunday in Kern County.

The news of the outage comes as the utility is in the process of restoring power to about 179,000 customers in Northern California. Power was restored to 99% of its customers on Friday, with the exception of Sonoma County where the Kincade Fire continues burning, the utility said.

Northern California inferno destroyed dozens of homes

About 89,000 people in Sonoma County have been ordered to evacuate due to the wind-driven Kincade fire.

"You cannot fight this (fire). Please evacuate," Sonoma County Sheriff Mark Essick told reporters.

The fire, burning northeast of Geyserville in Sonoma County, has burned 25,955 acres and was 10% contained as of Saturday evening, according to the California Department of Forestry and Fire Protection, or Cal Fire.

The blaze has destroyed 77 structures, including 31 homes, Cal Fire Division Chief Jonathan Cox told reporters Saturday evening.

Mandatory evacuations were expanded twice on Saturday. Officials said the prolonged wind event will lead to fire spreading rapidly and erratically.

"The fire intensity has the potential to overwhelm even the professionals," Cox said.

Forecasters are expecting winds of 30-55 mph with gusts of 60-80 mph beginning Saturday night, the National Weather Service said. The winds can blow down trees, power lines and made it difficult for most vehicles to travel, including those pulling trailers.

"This will be a long duration and potentially extreme/historic even across the North Bay," the weather service in San Francisco said in an advisory.