LOS ANGELES — Firefighters kept a wall of flames from descending mountains and entering coastal neighborhoods after a huge and destructive Southern California wildfire exploded in size, becoming the fifth-largest in state history.
Tens of thousands remained under evacuation orders Monday as the fire churned west through foothill areas of Carpinteria and Montecito, seaside Santa Barbara County towns about 75 miles northwest of Los Angeles.
Much of the fire’s rapid new growth occurred on the eastern and northern fronts into unoccupied areas of Los Padres National Forest, where the state’s fourth-largest fire burned a decade ago.
The Santa Barbara blaze, which had already destroyed more than 750 buildings, gutted six more in Carpinteria on Sunday, officials said. It’s just 15 percent contained after charring nearly 360 square miles of dry brush and timber.
‘‘We’re still anxious. I’m not frightened yet,’’ Carpinteria resident Roberta Lehtinen told KABC-TV. ‘‘I don’t think it’s going to come roaring down unless the winds kick up.’’
Forecasters said winds that fanned several fires across the region for a week were beginning to lose strength Monday.
Light gusts were pushing onshore, driving the flames back up hillsides and away from communities, Santa Barbara County fire spokesman Mike Eliason said. But the possibility of ‘‘unpredictable’’ gusts would keep firefighters on edge for days, he said.
Santa Ana winds have long contributed to some of the region’s most disastrous wildfires. They blow from the inland toward the Pacific Ocean, speeding up as they squeeze through mountain passes and canyons.
Environmental regulators warned people in parts of Santa Barbara, Ventura, and Los Angeles counties to stay indoors, avoid vigorous outdoor activities, and not do anything to stir up ash because of unhealthy air.
With the air thick with acrid smoke, even residents of areas not under evacuation orders decided to leave, fearing another shutdown of US 101, a key coastal highway that was closed intermittently last week.
Officials handed out masks to residents who stayed behind in Montecito, the hillside enclave that’s home to celebrities such as Oprah Winfrey, Jeff Bridges, and Drew Barrymore.
Smoke shrouded Rob Lowe’s home and the actor wore a mask as he livestreamed his family leaving on Sunday.
‘‘Praying for the people in my area,’’ he said on Instagram. ‘‘Hope everybody’s getting out safe like we are, and thanks for the prayers and thoughts. And good luck to the firefighters, we need you!’’
Talk show host Ellen DeGeneres tweeted that neighbors were helping each other and their animals get to safety.
‘‘I’m sending lots of love and gratitude to the fire department and sheriffs. Thank you all,’’ she wrote.
Meanwhile, containment increased on other major blazes in Los Angeles, Riverside, and San Diego counties. Resources from those fires were diverted to the Santa Barbara foothills.
Fires are not typical in Southern California this time of year but can break out when dry vegetation and too little rain combine with the Santa Ana winds. Though the state emerged this spring from a years-long drought, hardly any measurable rain has fallen over the past six months.
‘‘This is the new normal,’’ Governor Jerry Brown warned Saturday after surveying damage from the deadly Ventura fire. Brown and experts said climate change is making wildfires a year-round threat.
High fire risk is expected to last into January.
Despite the size and number of wildfires burning in the region, there has only been one confirmed death: that of a 70-year-old woman, who crashed her car on an evacuation route in Santa Paula.
