Utility equipment is suspected in the Easy fire and others.

California regulators said on Wednesday that they were investigating whether Southern California Edison’s equipment had played a role in the Easy fire in Ventura County, after the utility said it found “circuit activity” close to the time the fire was reported.

The disclosure was one of several on Wednesday in which officials said they were eyeing the hardware of California utilities in connection with fires, including at least four that ignited in the Bay Area on Sunday.

PG&E, the private utility, shut off power to nearly 1 million customers this week. It was the largest public safety blackout in California history and comes after the company’s power lines caused a fire in 2018 that killed 85 people and destroyed nearly 19,000 buildings in Northern California.

By late on Wednesday, PG&E said it had restored power to about 95 percent of those customers, leaving about 53,000 business and residential customers still in the dark, a figure that translates to roughly 130,000 people affected. Power was completely restored in 23 of the 37 counties that were affected by the shut-offs, the company said.

Despite the company’s precautions, a vegetation fire broke out under its power lines in Bethel Island, Calif., on Sunday and grew to the size of a football field, threatening a new housing development, before being brought under control, the East Contra Costa Fire Protection District said. The district said another fire that prompted some evacuations in Oakley, Calif., started after PG&E equipment cast sparks 200 yards away.

PG&E told California regulators it was also investigating whether a transformer and an open wire were responsible for two fires in Lafayette, Calif., on Sunday.