(New throughout, adds details)
By Steve Gorman
LOS ANGELES, Oct 9 (Reuters) - Electricity was shut off to more than 500,000 California homes and businesses on Wednesday as Pacific Gas and Electric Co imposed a planned power outage of unprecedented scale to reduce wildfire risks posed by high winds and hot, dry weather.
A second phase of the "public safety power shutoff" was slated to begin at midday, extending cutoffs to another 234,000 customers, the utility said, and it was considering a third phase for 42,000 more homes and businesses.
The outages were planned for communities across 34 of the state's 58 counties, all in PG&E's service area in northern and central California.
Sustained gale-force winds were forecast to linger through midday Thursday, with isolated gusts of up to 70 miles per hour, the utility said in announcing the shutdown. Once power is turned off, it cannot be restored until winds subside, allowing PG&E to inspect equipment for damage and make repairs, the company said.
The utility has warned residents to prepare for outages that could last several days, but spokeswoman Kristi Jourdan said PG&E expected to restore electricity to most customers "within 24 to 48 hours after the weather has passed."
Ultimately the measure could leave nearly 800,000 homes and businesses, comprising millions of people, without electricity, the largest precautionary electricity shutoff PG&E has undertaken. Of six previous such power cuts, the largest occurred a year ago and affected 60,000 customers.
Ahead of Wednesday's shutdown, customers were urged to stock up on flashlights, fresh batteries, first-aid supplies and cash, and to plan for healthcare needs requiring refrigerated medications or electrical devices.
The utility said it opened 28 community centers across the planned outage zone to furnish restrooms, bottled water, battery charging and air-conditioned seating during daytime hours.
The California Department of Forestry and Fire Protection (Cal Fire) said "red-flag" warnings were posted across the state for what was shaping up to be the strongest wind event so far this season.
PG&E has come under increased scrutiny in recent years over maintenance of transmission wires and other equipment implicated in major wildfires.
In May, state fire investigators determined that PG&E transmission lines caused the deadliest and most destructive wildfire on record in California, last year's wind-driven Camp Fire that killed 85 people in and around the town of Paradise.
Cal Fire likewise concluded that PG&E power lines had sparked a separate flurry of wildfires that swept California's wine country north of San Francisco Bay in 2017.
PG&E filed for bankruptcy in January 2019, citing potential civil liabilities in excess of $30 billion from the fires.
Utility officials said they had placed dozens of helicopter crews and hundreds of extra ground personnel on standby for inspections and repairs once the winds die down in order to restore power as quickly as possible. (Reporting by Steve Gorman in Los Angeles; additional reporting Jim Christie in San Francisco and Rich McKay in Atlanta; editing by Larry King and David Gregorio)
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