PG&E plans a 10-year effort to put power lines underground to reduce fire risk.

Pacific Gas & Electric announced an ambitious plan on Wednesday to put 10,000 miles of its power lines underground to prevent the kind of wildfires that led the utility to bankruptcy court in 2019.

The power company, California’s largest electricity provider, said the project would aim first at areas most vulnerable to wildfires and expand throughout its service territory, which includes 5.5 million electric customers in Northern and Central California.

PG&E’s announcement followed a preliminary report over the last week to state regulators that its equipment may have caused the Dixie Fire, one of the state’s largest blazes, which has burned at least 85,000 acres. The fire is spreading in Butte County, where the utility’s equipment caused a fire that destroyed the town of Paradise and killed 85 people in 2018.

Although utilities across the country have increasingly moved their power lines underground, none have proposed a project on the scale of PG&E’s plan.

“We need you to know that we are working night and day to solve this incredible problem,” Patricia K. Poppe, chief executive of PG&E Corporation, the utility’s parent.

PG&E operates more than 106,000 miles of electric distribution lines and more than 18,000 miles of longer-distance transmission lines, according to its website. The company had been proposing to install some of its power lines underground in the Butte County area but not on the scale of its announcement.

Mark Toney, executive director of the Utility Reform Network, which represents consumers before the California Public Utilities Commission, said that reducing wildfire risk is a priority but that the utility must develop a plan that would fund the huge project without overburdening ratepayers, who already are paying enormous costs. The project could cost $40 billion based on about $4 million per mile estimated for underground power line proposals that PG&E has submitted to state regulators, Mr. Toney said.

“We’d be living in a world where only the wealthy could afford electricity,” Mr. Toney said. “PG&E needs a plan to reduce the most risk possible at the least cost possible to ratepayers.”

The company said that it could install about a quarter-mile of power lines underground a day but that it aimed to increase that to 1,000 miles or more a year to prevent fires.

PG&E has been a focus of the impact of climate change since a series of record-setting wildfires began burning through Northern California in 2017, several of them caused by the utility’s equipment.

The utility has taken several steps to prevent fires, including installing equipment to monitor weather conditions and to allow lines to be shut off remotely. But the effectiveness of those efforts has increasingly come under question, particularly after the company reported that its equipment might have caused the Dixie Fire. The wildfire season has months to go before its peak.

State regulators and the courts have fined the utility billions of dollars for failing to maintain its equipment and causing fires. The company, which emerged from bankruptcy last year after amassing $30 billion in liability related to wildfires, pleaded guilty to 84 counts of involuntary manslaughter related to the Paradise fire.

It was the second felony conviction for the utility. In 2016, PG&E was found guilty of federal charges related to a gas pipeline explosion six years earlier in the San Francisco suburb of San Bruno that killed eight people.