Wrightwood, California - A wildfire in the hills near Los Angeles exploded overnight, torching dozens of homes as its footprint swelled 1,000% by Wednesday.

The Bridge Fire is one of three out-of-control blazes that have erupted around the US' 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 and 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.

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"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 by Tuesday had grown to around 4,000 acres (1,600 hectares).

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. Resort staff said the resort was largely unscathed.

"All the main lifts and buildings survived with little to no damage," a social media post said.

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," he told reporters.

He said all three were understood to be in good health.

To the southeast of Los Angeles, the Airport Fire was continuing to grow Wednesday, racing through vegetation and damaging a number of homes.

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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 consumed nearly 35,000 acres (14,000 hectares).

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

Firefighters were battling the blaze from the air as ground crews sought to establish containment lines, trying to create breaks in the vegetation to prevent the fire from spreading further.

Police in San Bernardino County arrested Justin Wayne Halstenberg (34) late Tuesday on suspicion of arson in connection with the fire.