SAN FRANCISCO (AP) - Authorities ordered at least 50,000 residents to evacuate towns near a massive Northern California wildfire Saturday, and the state's largest utility announced power shut-offs for an estimated 2.35 million people due to forecasts of severe winds and extreme fire danger.

Two previous electricity shut-offs in recent weeks were carried out amid concern that gusty winds could disrupt or knock down power lines and spark devastating wildfires.

Some gusts this weekend might reach 75 mph or higher as part of a "historic" wind event, the National Weather Service warned.

Pacific Gas & Electric said a new wave of blackouts would be implemented in stages through Saturday afternoon and evening, affecting about 940,000 homes and businesses in 36 counties for 48 hours or longer. The city of San Francisco was not in line for a blackout; shut-offs were ordered for most of the rest of the San Francisco Bay Area, the wine country to the north and the Sierra foothills.

The entire communities of Healdsburg and Windsor were ordered to evacuate ahead of strong winds that could lead to erratic fire behavior near the blaze burning in wine country.

The Sonoma County Sheriff's Office said it would be the biggest evacuation in the county in more than 25 years.

"The winds are expected anywhere between 8 p.m. and midnight and from all reports they're expected to be extremely strong," said Brian Vitorelo with the California Department of Forestry and Fire Protection.

PG&E's shut-off order came as firefighters battled fires in Northern and Southern California.

A blaze Thursday destroyed at least six houses in the Santa Clarita area near Los Angeles and led to evacuation orders for up to 50,000 residents, although most were allowed back home after Santa Ana winds began to ease. The Tick fire was 25% contained.

To the north, firefighters raced to make progress against a blaze near Geyserville in Sonoma County before ferocious "diablo winds" returned. The Kincade fire had burned 49 buildings, including 21 homes, and swept through nearly 40 square miles (104 square kilometers) of the wine-growing region. It was 10% contained by Saturday morning.

A firefighter and two civilians were injured when they were overwhelmed by flames as they tried to evacuate from approaching flames, authorities said.

"The firefighter was forced to deploy his fire shelter, where he shielded them from fire," Cal Fire said in a statement. After the flames passed, all three were hospitalized with non-life-threatening injuries, the statement said.

Several thousand people living in small communities in neighboring Lake County were warned to be ready to evacuate if an order is given. The area was the scene of a 2015 wildfire that killed four people and burned nearly 2,000 homes and other buildings.

No cause has been determined for any of the current fires, but PG&E said a 230,000-volt transmission line near Geyserville had malfunctioned minutes before that fire erupted Wednesday night.

The utility acknowledged that the discovery of the tower malfunction had prompted a change in its strategy.

"We have revisited and adjusted some of our standards and protocols in determining when we will de-energize high-voltage transmission lines," Andrew Vesey, CEO of Pacific Gas & Electric Co., said at a briefing Friday.

The weekend forecasts detail what could be the strongest winds of the year coupled with bone-dry humidity. Many homes and business facing power shut-offs were far from current fires. PG&E cast the blackouts as a matter of public safety, aimed at preventing the kind of blazes that have killed scores of people over the past couple of years, destroyed thousands of homes, and ran up tens of billions of dollars in claims that drove the company into bankruptcy.

"Any spark, from any source, can lead to catastrophic results," Vesey said. "We do not want to become one of those sources."

The possible link between the wine country fire and a PG&E transmission line contained grim parallels to a catastrophic fire last year that tore through the town of Paradise, killing 85 people and destroying thousands of homes in the deadliest U.S. fire in a century.

State officials concluded that fire was sparked by a PG&E transmission line.

Many residents in the blackout-targeted region had barely recovered from a previous shut-off.

Jon Robinson, 52, of Rough and Ready, said the earlier shut-off put him in the hospital for several days for the stomach flu. He'd been tending to his sick grandson and got worn down between that and taking care of animals on his ranch.

Robinson was unsure if his family, who moved to California seven years ago, will remain in the state much longer.

"Before this, we planned on staying," he said. "But I'll tell you what, it's just too nerve-racking."

For many people affected by the shut-offs, there have been painful business-related losses.

In Newcastle, about 30 miles (48 kilometers) northeast of Sacramento, 65-year-old Sukhwinder Singh works the cash register at Quality Market, a local convenience store. During the previous outage, Singh said he worked in the dark, but customers did not want to buy his warm soda and melted ice cream. He estimates he lost about $1,100 in sales and products. Singh has a generator now but said he can't keep it running all night when the store is closed.

"I don't know how we can pay the bills at the end of the month," he said.

In Loomis, about 5 miles (8 kilometers) from of Newcastle, Scott Paris estimates that he lost about $20,000 in business proceeds when he had to shut down his High-Hand Nursery and Cafe when PG&E turned off the power earlier this month. And that was just for about 24 hours during a weekday.

This time he expects to lose power on a weekend, when he might typically do $50,000 to $60,000 worth of business on a beautiful fall Sunday.

"We're scrambling to get enough generators," he said. "If this is the new normal, it's going to drive up a lot of costs. It drives up stress."

In Marin County, just north of San Francisco, the sheriff's office warned that a power shut-off would likely knock out some traffic lights. Intersections with inoperable lights should be treated as a four-way stop, the office said.

Even before the new blackout order, the University of California, Berkeley announced it was canceling all Saturday afternoon classes, as well as other indoor events and activities scheduled through Sunday.

A Florida utility, Florida Power & Light, announced it was sending 100 line workers and support staff to help PG&E restore power to areas with outages caused by the wildfires.

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