Critics of PG&E, including some state lawmakers, have said that the company may have blacked out more customers than necessary to reduce the risk of wildfires. State Senator Jerry Hill , a Democrat from the Bay Area, sent a letter venting his frustration to the California Public Utilities Commission, which will review PG&E’s actions.

“Today marks an unprecedented turn in the history of electricity service in California,” Mr. Hill wrote. He said that safety shut-offs “must be a surgical, last resort measure.”

Does this have anything to do with the company’s bankruptcy?

Not directly. The power shut-offs are part of PG&E’s wildfire safety program, which the utility developed in response to state rules put in place after the devastating 2017 wildfires in the Napa and Sonoma wine country.

Lawmakers required the state’s utilities to submit plans to help prevent wildfires. PG&E proposed several measures, including shutting off power when wildfire risk was elevated. Another utility, San Diego Gas & Electric, has used this approach for years.

The safety measures were intended to prevent wildfires and to keep the utilities from financial ruin by limiting their liability for the damage caused by their equipment. In its bankruptcy case, PG&E has been seeking to resolve wildfire damage claims from thousands of homeowners, insurance companies and others.

How long will the blackout last?

PG&E’s internal models and forecasts from the National Weather Service indicate that the extreme weather conditions could last through Friday. PG&E said it had restored service to about 126,000 customers. But 600,000 were still without power Thursday morning, and thousands more could still lose electricity.

Before restoring power, PG&E will have to inspect its equipment for damage and make any needed repairs. That process cannot begin until the severe weather has passed, the company said.