SAN FRANCISCO — A deliberate power outage that spanned large parts of Northern California on Wednesday sent hundreds of thousands of people scrambling for gasoline and other essentials as strong, gusty winds and months of dry weather put the state on alert for wildfires.

The state’s largest power utility, Pacific Gas & Electric, said it had cut power to 500,000 customers soon after midnight. A second round of cuts affecting 250,000 more customers in the hills surrounding the San Francisco Bay Area had been scheduled for noon but was delayed.

“It’s all dependent on weather conditions,” said Jeff Smith, a spokesman for the company. Mr. Smith could not give a new time for the next round of blackouts, though a Police Department in the East Bay of San Francisco said the new power shut-off time was 8 p.m.

While PG&E said that hundreds of thousands of customers would lose power, an entire apartment building can be considered a single customer. Once the two phases are complete, around 2.5 million people will be without electricity, according to one estimate.