SAN FRANCISCO -- Electricity is starting to come back on for communities across Northern California.
PG&E has restored power to more than 200,000 customers so far. Crews are now inspecting power lines in all 34 counties impacted by the shutoffs.
The utility company says the process may take a few hours or a few days. There are still about 600,000 customers without power.
Nearly 500,000 Pacific Gas & Electric (PG&E) customers in Northern California were in the dark starting at midnight Wednesday as the company began shutting off power in an effort to help prevent starting a wildfire.
A total of 800,000 customers were affected by the shutoff, Sumeet Singh, vice president of the company's Community Wildfire Safety Program, said.
The NorCal shutoff comes as San Diego Gas & Electric warned some 30,000 customers in high fire-risk areas Tuesday that they could be impacted by a round of power shutoffs due to strong winds in Southern California. That number was down to 17,771 by Friday morning.
Several school districts and a major university have canceled classes, while traffic tunnels and public transit amenities also may be affected, officials said.
Forecasters warn that many parts of Northern California are under extreme fire weather danger, with windy and dry conditions forecast.
"We implement this public safety power shutoff as a last resort," Singh said in a Tuesday news conference.
It could take several days to restore power, Singh added, as the company will first conduct safety inspections once the widespread wind event is over.
PG&E has come under criticism in recent years for the role of its equipment in a series of catastrophic wildfires across the state, including the deadly 2018 Camp Fire. The utility has agreed to pay billions of dollars in damages.
Who is impacted
On Monday, San Jose Mayor Sam Liccardo urged residents to prepare to be without power for as long as seven days.
The shutoff spans portions of 34 northern, central and coastal California counties, he said.
The California Department of Transportation has been working with the utility company to secure backup power generators to keep the Caldecott Tunnel in Contra Costa and Alameda counties and the Tom Lantos Tunnel in Pacifica open, spokesman Bart Ney told CNN.
School officials canceled classes Wednesday. Closures affect all schools in the Napa Valley Unified School District, San Leandro Unified School District and Cloverdale Unified School District, plus Bennett Valley Union School District schools in Strawberry and Yulupa.
UC Berkeley also canceled classes in response to the power shutoff.
The Governor's Office of Emergency Services has activated the State Operations Center to help counties affected in the shutoff, it said.
"Cal OES Fire, Law Enforcement, Inland Region and Coastal Region personnel are currently working with various response agencies to address all emergency management, evacuation and mutual aid needs," the agency said in a news release.
Why the weather conditions are important
The conditions that are being forecast for portions of the state "historically have led to catastrophic wildfires," the utility giant's senior meteorologist, Evan Duffey, said in the news conference.
And this, he said, is by all metrics "forecast to be the strongest offshore wind event since October 2017."
The National Weather Service has warned of strong winds and low humidity running over dry vegetation, which the service said acts as "fuels."
"This is a recipe for explosive fire growth, if a fire starts," the weather service said. "Have your go pack ready."
The service issued red flag warnings starting early Wednesday morning across the North Bay Mountains and Valleys, East Bay Hills and East Bay Valleys. The warnings mean "warm temperatures, very low humidities, and stronger winds are expected to combine to produce an increased risk of fire danger," the service said.
The strong winds began Wednesday morning, lasting until Friday morning, Duffey said during the news conference.
Could take days to restore power
PG&E has activated an emergency operation center that is staffed at all hours, Singh said.
Some of the utility company's customers may have their power shut off "even though the weather conditions in their specific location are not extreme," he said during the news conference.
"(That's) because of the interconnected nature of our electrical grid and the power lines working together to provide electricity to cities, counties and regions," Singh said.
And power will take several days to restore as the company inspects its equipment to make sure there's no damage, he said.
"We very much understand the inconvenience and difficulties such a power outage would cause and we do not take or make this decision lightly," he said. "This decision ... was really focused on ensuring that we're continuing to maintain the safety of our customers and our communities."
PG&E has previously said it is "probable" that its equipment started the 2018 Camp Fire -- the state's deadliest and most destructive blaze -- when a power line touched nearby trees. California's Department of Forestry and Fire Protection found PG&E responsible for the fire, which killed 85 people and destroyed thousands of structures.
The utility announced in September it had reached an $11 billion settlement with insurance companies for claims stemming from the devastating 2017 wildfires in Northern California and the Camp Fire. In June, PG&E paid $1 billion in damages to local governments for blazes linked to its power lines, poles and other equipment.