A wildfire ravaging the hills near Los Angeles had swelled in size by over 1,000 percent by Wednesday, torching dozens of homes and prompting a state of emergency.

The Bridge Fire is one of three out-of-control blazes that have erupted around the United States' second-biggest city, fueled by a punishing heat wave and fanned by gusting winds.

Authorities issued widespread evacuation orders as the fire tore through the towns of Wrightwood and Mt Baldy, destroying at least 33 homes, several cabins, and racing through a ski resort.

"We live in the canyon so that fire was coming right in there, and you couldn't take anything out of there," local resident Jenny Alaniz emotionally told broadcaster KTLA.

The wildfires have wreathed Los Angeles in choking smoke.

"I got the dogs out. Our house is gonna burn," she sobbed.

An AFP journalist in Wrightwood witnessed the aftermath of the fire, where the charred shells of buildings and vehicles stood shrouded in smoke. The fire broke out early Sunday afternoon in Angeles National Forest north of Los Angeles, and initially remained fairly small.

But by Wednesday afternoon it had roared to 49,000 acres (20,000 hectares), fueled by thick brush that carried the flames into the San Bernardino County community of Wrightwood and the Mountain High ski resort.

Three trapped

Los Angeles County Sheriff Robert Luna said three people -- including one of his deputies -- were trapped by the fire in a remote area near Mt. Baldy.

He said thick smoke and blocked roads were hampering the rescue effort.

"Our air rescue crew is working to hoist them out once the smoke clears, and LA County Fire is also trying to get a four-by-four vehicle to get them out," Luna told reporters.

He said all three were understood to be in good health. The Bridge Fire has torn through Wrightwood, destroying a number of homes and forcing evacuations.

Southeast of Los Angeles, the Airport Fire continued to grow Wednesday, racing through vegetation and damaging several homes.

Cal Fire, the statewide fire agency, said seven people had been hurt in the blaze, which has now charred more than 22,000 acres (8,900 hectares).

The blaze erupted on Monday and began racing up canyons and hillsides, including Santiago Peak, which is home to radio and television broadcast towers, though the fire appeared to have left them undamaged.

The flames were also hurtling downslope toward Lake Elsinore, with video from the area showing some structures and vehicles consumed by fire.

Dramatic photographs taken by an AFP journalist show towering walls of flame.

Northeast of Los Angeles, the Line Fire has now burned nearly 35,000 acres.

A number of mountain communities were ordered to evacuate, in an area popular with tourists, and several major access roads were blocked.

Police in San Bernardino County have arrested a man in connection with the fire.

Justin Wayne Halstenberg, 34, from Norco was detained late Tuesday on suspicion of starting the blaze.

'Herculean effort'

California Governor Gavin Newsom, who has declared a state of emergency in response to the fires, visited the command post at the Line Fire on Wednesday.

"California is deploying every available resource to combat these devastating fires, and we'll continue to work in lockstep with federal and local partners in this herculean effort," he said.

More than 5,700 emergency personnel are responding to the three fires, his office said, along with dozens of aircraft and over 500 fire engines.

"We are deeply grateful to all the heroic firefighters and first responders... working 24/7 to keep Californians safe," Newsom said.

A persistent heat wave that has gripped much of southern California for a week was easing Wednesday, and officials were hopeful that lower temperatures might make the battle against the fires easier.

Wildfires are a natural part of the wilderness cycle and are not unusual in California and other parts of the US West at this time of year.

But after two relatively mild fire years, 2024 is shaping up to be significant.

A couple of very wet winters generated abundant growth of vegetation, which has now dried out after a long, hot summer, leaving behind lots of fuel.