LOS ANGELES — Firefighters across California raced to tamp down major wildfires Tuesday as another round of fierce Santa Ana winds headed to the state, where tens of thousands of people had already been driven from their homes and hundreds of thousands more were without power.

Fire crews made progress Tuesday against the Getty fire near the J. Paul Getty Museum in one of Los Angeles' ritziest areas. The fire had consumed 656 acres by Tuesday afternoon, and containment had risen to 15 percent, fire authorities said.

The blaze appeared to have been sparked at about 1:34 a.m. Monday in the Sepulveda Pass, not far from the museum, when a tree branch that had been snapped off by intense winds struck power lines, caught fire and dropped onto a brush-covered hillside below, the Los Angeles City Fire Department said.

Thanks to the progress Tuesday, a mandatory evacuation zone in West Los Angeles shrank to cover about 7,000 structures, including homes and businesses, officials said. The evacuation zone included homes belonging to some of Southern California's richest and most famous residents, such as former Gov. Arnold Schwarzenegger and Los Angeles Lakers superstar LeBron James.

At least 12 homes had been destroyed, and five others had been damaged, fire officials said Tuesday afternoon.

A "remarkable and dangerous" Santa Ana wind event expected Tuesday night was forecast to make matters worse, delivering gusts of up to 70 mph in much of Southern California — and as high as 80 mph in mountain areas.

The National Weather Service said the renewed fire threat in parts of Ventura, Los Angeles, San Bernardino, Orange and Riverside counties would be "extremely critical," a description it has rarely used before. It said conditions would be "as dangerous for fire growth and behavior as we have seen in recent memory."

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The weather service said that all of the elements of a strong Santa Ana wind event were lining up and that "most of these elements are very strong."

"Unlike our previous events this October, this will not be a one day event," it said.

Tinder-dry brush in the region hasn't seen rain for months.It's been 125 days — about four months — since the last rain fell downtown and 95 days since it rained at Los Angeles International Airport.

"Our goal today will be to increase containment as much as possible. That is our primary objective," city Fire Chief Ralph Terrazas said. "It only takes one ember to blow downwind and start another fire."

Gusts topping 40 mph were already raking across Northern California, where the state's largest utility, Pacific Gas & Electric Corp., or PG&E, began shutting off power to about 600,000 customers Tuesday morning — the fourth massive round of rolling blackouts in the region in less than a month.

The utility, which provides power across much of Northern California, has used rolling blackouts in fire-prone areas where downed lines and faulty transmission towers have been known to spark wildfires, including last year's Camp fire, the state's deadliest, which killed 85 people.

PG&E has been turning the lights back on since Monday for some of the hundreds of thousands of customers whose power was cut off in the third blackout over the weekend. The two events overlapped, however, and almost 975,000 homes and businesses, roughly equivalent to almost 2.5 million people, have been without at some point since the weekend, PG&E said.

By Tuesday night, about 435,000 customers were without power, it said.

Winds through Wednesday weren't expected to be as strong as in Southern California, the weather service said, but they were still likely to fuel "critical" fire conditions similar to those that occurred when the Kincade fire ignited last week north of San Francisco.