La Verne, Calif. ? A wildfire in the foothills above Los Angeles jumped from 8,000 acres to 12,000 acres in just a few hours Tuesday, sending smoke pouring over the sprawling metropolitan area and triggering public health warnings.

The fire, spread across 11 miles of the San Gabriel Mountains, has destroyed 44 cabins and homes and threatens hundreds of others. Flames raged unchecked as firefighters worked in rugged canyon terrain against erratic winds and triple-digit temperatures.

Firefighter Steve Johnson of the U.S. Forest Service sets a backfire ahead of approaching flames at a brush fire north of Glendora, Calif. The wildfire grew to 12,000 acres Tuesday as firefighters struggled to contain the flames.

Some two dozen aircraft dropped water and fire retardant on the fire, which authorities said had the potential to grow to 20,000 acres.

Fear of new fires led officials to close the 650,000-acre Angeles National Forest, which includes the mountains, to recreation.

“We certainly can’t afford another fire,” said Darren Drake, a fire spokesman. “This has got our hands full.”

The fire threatened upscale homes in La Verne, San Dimas and other suburbs.

Voluntary evacuations were called for at least 500 homes and 1,000 people. A mandatory evacuation was ordered for 77 recreational cabins in San Dimas Canyon, and more than 200 youths were taken out of two juvenile detention camps.

Authorities were investigating the cause of the fire that began Sunday.