Outages began mid-morning, and about 12,900 customers had lost power by 11 a.m., including in Los Angeles, Ventura, San Bernardino and Kern Counties. Nearly 174,000 customers across nine counties have been notified about possible shut-offs, said Mary Ann Milbourn, a spokeswoman for the utility.

“It’s all about Mother Nature,” Ms. Milbourn said. “We know this wind event is going to last into tomorrow.”

Firefighters were responding to at least two blazes in Riverside County, one of which appeared to be in a mobile home park. That fire had spread to 200 acres by Thursday afternoon, according to the California Department of Forestry and Fire Protection.

‘This isn’t the end of this.’

When Ben Faus went to sleep Wednesday night at his home in the foothills above the Monterey Bay, he knew there was a chance his power would go out. About 3 a.m., when he was jolted awake because his electric sleep apnea breathing machine stopped working, he knew the blackout had arrived. “All of a sudden, I was like, ‘I can’t breathe,’” he said.

Mr. Faus, 74, is a retired pharmacist who has lived with his wife in the Central Coast town of Aptos for three decades. On a cold and clear Thursday morning, they were among tens of thousands of residents in Santa Cruz County, as well as large metro areas in San Jose and Oakland, who woke up to a blackout as part of PG&E’s fire-precaution plan.

In a region where officials this week issued a red-flag fire warning for the Santa Cruz Mountains, Mr. Faus said he appreciated the effort to prevent sparks but the utility was not doing enough to keep residents informed of when and how long power would be turned off. “I can see the reason they’re gun-shy, but I think they’re overdoing it,” Mr. Faus said. “I almost feel like they’re trying to show people just how vital they are.”

Outside a Safeway grocery store just after dawn, dead traffic lights caused backups. Commuters toting travel mugs from homes without power begrudgingly got back into their cars without coffee when security guards informed them the store would open late.