OAKLAND, Calif. — One of the nation’s largest utilities began shutting off power early Wednesday to what could eventually be nearly 1 million Californians, using a relatively new and disruptive method to lessen wildfire risk in a state of intensifying weather extremes.

The intentional shut-off encompasses more than half of the state’s 58 counties and spans much of Northern California, where two of the deadliest fires in state history have occurred in the past two years. It is the most extensive planned power outage ever employed in California and represents a fresh, expensive inconvenience to residents of a state confronting the sharpening consequences of a changing climate.

Pacific Gas & Electric, the utility behind the power shut-off, was found responsible for sparking one of those fires, which blazed through Paradise, Calif., last year, killing 85 people and turning 14,000 homes to ash in the Sierra Nevada foothill town. The company has since filed for bankruptcy protection in the face of billions of dollars in liability claims.

PG&E was among the last of the state’s utilities to use the “public safety power shutoff,” as the planned outages are known. Power companies here have the right to shut off electricity when the wind, temperature and humidity align to create high-risk fire conditions, although such decisions are reviewed by the California Public Utilities Commission.

“We know how much our customers rely on electric service and the impacts these events can have on them, their families, businesses, and communities — including the use of medical equipment and refrigeration,” PG&E wrote in a report to the commission last month on its use of power shut-offs. “We will only consider proactively turning off power when the benefits of de-energization outweigh potential public safety risks.”

But there is also an element of political negotiation in the shut-offs, which in this case was explained by PG&E as the result of the stiff, dry winds expected to whip up overnight here and which, in the past, have been the driving force behind the state’s worst fires.

In Northern California the wind, which blows warm from the northeast, is known as a Diablo. Forecasts for late this week call for gusts as strong as 45 mph.

PG&E has sought in recent years to loosen California’s liability standards, which hold utilities liable for any damage caused by fires started by its equipment, whether the company is found negligent or not. The principle, known as “inverse condemnation,” is among the strictest in the nation.

Despite heavy lobbying by the utilities, California lawmakers had refused to change that standard in recent legislative sessions. But this year lawmakers loosened it slightly to allow a lower liability threshold for utilities that first complete billions of dollars in safety improvements to power lines, transformers and other equipment.

“When the power goes out, it’s fun to sit around and fantasize about the many ways you will oppose any legislation or initiatives that are favorable towards PG&E,” wrote John Holland, a Berkeley, Calif., resident facing the prospect of a power shutdown, in a Tuesday afternoon tweet.

PG&E has 16 million customers, the majority of them in Northern California. The company has begun a campaign of television advertising concerning fire safety. The spots include animated illustrations of how to create “defensible spaces” around homes, jargon that has gradually crept into California’s daily conversation.

Across the state, neighborhoods organize meetings to gather information about which residents would need extra help during intentional power shut-offs, who has generators, and whose medical issues would be exacerbated by a blackout.

This shutdown may affect about 800,000 customers who live in a crescent around San Francisco, residents of the state capital, Sacramento, and much of California wine country. The northern Sierra Nevada also falls within the planned shut-off area.

Utilities attempt to give a 48-hour warning before a planned power outage, allowing customers some time to prepare for what could be a long time without electricity. The extent of this outage, the utility has warned, could mean that it will take days to turn the power back on across the affected area once the winds have calmed and temperatures cooled.

Power shut-off warnings take a worst-case approach initially, and as it nears, the area affected often shrinks. In this case, the opposite occurred as wind forecasts changed to show the Diablo starting earlier and blowing more broadly. PG&E extended the area where conditions might prompt it to turn off the power, including in Marin County just north of San Francisco.

Even short-lived outages have proven onerous — and expensive — to state residents. In rural California, already butchered meat, grapes and avocados, among other products, have spoiled without refrigeration during recent power shut-offs and emergency generators are costly to buy and run. They also pose a fire risk.

Here in Oakland, a city whose hills burned in 1991, killing 25 people and destroying more than 2,800 homes, the sun set without a breath of wind.

The city falls within the planned shut-off area. But the evening was cool, if also dry, and the threat of fire remained undetectable.