“What we find ourselves experiencing is a historic wind event,” Andy Vesey, head of the Pacific Gas & Electric utility unit, said at a press conference Saturday night. The shutoff is a “last resort to make sure that in these conditions our operations will not create a major public safety issue. That’s why we do it.”

The start times in some cases were pushed back because anticipated winds — which are forecast to gust as high as 65 to 80 miles per hour (129 kilometers per hour) — didn’t arrive as early as initially forecast.

It’s the third time this month that PG&E has resorted to mass blackouts to avoid wildfires. The San Francisco-based company has been taking more extreme measures since its equipment sparked blazes in 2017 and 2018, saddling it with an estimated $30 billion in liabilities and forcing it into bankruptcy. The shutoffs have ignited a debate over how far California is willing to go to prevent fires in an increasingly warm and dry climate. Despite the power cuts, blazes continue to burn.

In Southern California, Edison International is warning that it may cut service to more than 160,000 customers. Sempra Energy’s San Diego Gas & Electric said it has no emergency shutoff plans at present.

Weather models show the wind storm could be the most powerful to hit California in years, according to PG&E.

Wildfires are already raging at both ends of California, prompting Governor Gavin Newsom to declare a state of emergency Friday. The Tick blaze near Los Angeles forced tens of thousands of evacuations. And north of San Francisco, the Kincade fire is raging in the vineyards of Sonoma County, triggering a historic evacuation. It had destroyed at least 77 structures and burned more than 25,000 acres as of Saturday night.

The Sonoma County fire was reported minutes after a PG&E transmission line in the area malfunctioned late Wednesday. Firefighters have not determined the cause of the blaze. PG&E’s shares plummeted 31% Friday to $5, a record low. Shares of Edison fell 8.5% as fires burned in its Southern California service territory.

On Saturday, Sonoma County Sheriff Mark Essick implored residents to leave immediately before the storm causes the fire to grow even more rapidly. “We’d like to get you out while we still have power and we still have communications,” he said.

All told, there’s about $12 billion worth of property within a mile of the active fires, said Chuck Watson, a disaster modeler with Evenki Research.

The prospect of more liabilities from wildfires is especially vexing for PG&E. Since filing for Chapter 11 in January, the judge overseeing the case has warned that another big blaze would upend the utility’s bankruptcy and potentially wipe out shareholders. Any claims from new fires sparked by PG&E would have to be paid out first — and in full — before those from previous blazes get a dime.

The winds are arriving at a precarious moment. California receives almost no rain during its summer, and a five-year drought earlier this decade killed millions of trees that can now easily ignite. Recent winds have dried out grasses and shrubs even further.

And the threat won’t end this weekend: Another front is expected to move in through Tuesday, bringing back strong, dry winds and once again raising the risk of wildfires spreading uncontrollably.

“We may have another weather system — not with this intensity– that may hit us early or middle of next week,” Vesey said.