A car drives under Interstate 5 as flames leap on the nearby hillside during a wind-driven brush fire in the northern foothills of Los Angeles on Saturday. (Dan Steinberg/Associated Press)

Thousands of people fled to safety Saturday as winds gusting up to 120 km/h fanned a new wildfire in the foothills just north of Los Angeles.

The blaze destroyed 500 mobile homes in Sylmar community, which is perched on the hillsides above the San Fernando Valley. No deaths were reported, but the L.A. police Chief William Bratton expressed concern that authorities might find bodies among the ashes.

Most people who live in the park are senior citizens.

"We have almost total devastation here in the mobile park," fire Capt. Steve Ruda said. "I can't even read the street names because the street signs are melting."

A burned resident was in serious condition, and four firefighters were treated for minor injuries. Emergency crews are waiting for the ground to cool before bringing in search dogs, Bratton said.

The 3,200-hectare blaze, which broke out late Friday, was only 20 per cent contained by Saturday evening. The fire consumed nine single-family homes and a number of other structures in Sylmar, on the edge of the Angeles National Forest.

Winds began to decrease in the afternoon and were expected to lessen even further overnight, although humidity is expected to remain low.

At least 20 people have been injured as separate fires burned in coastal Santa Barbara and around inland Riverside County, just outside L.A.

A Los Angeles County fire department helicopter drops water on a wildfire in the Sylmar area. Some aircraft were grounded Saturday because of high winds. (Mark J. Terrill/Associated Press)

Mayor Antonio Villaraigosa signed a local emergency order just before 8 a.m. PT Saturday. California Gov. Arnold Schwarzenegger has also issued a state emergency declaration. About 10,000 people, including residents of the mobile home park, are under evacuation orders, according to fire officials.

Villaraigosa urged people in L.A. to conserve electricity after two power lines in the northern San Fernando Valley stopped working. Some people in the fire area reported hearing transformers exploding.

"We may have to move to rolling blackouts. I understand the temperatures are going to be close to 100 F (37 C) today, so folks, please conserve energy. Do not wash today. Conserve your power as much as possible," he said.

The mayor said "absolutely atrocious" Santa Ana winds have helped spread the fire to more than 10 square kilometres.

Rows of houses gutted

The wind-driven blaze skipped over canyons and two highways. Aerial footage from television helicopters showed rows of houses gutted in one subdivision.

The Sylmar fire also surrounded Olive View-UCLA Medical Center around 1:30 a.m. local time and caused an electricity outage, forcing officials to evacuate about 200 patients.

The hospital's power and backup generators also failed, and emergency room staff had to keep critical patients alive with hand powered ventilators. A few babies were rushed out in ambulances to another hospital.

About 130 kilometres to the west, firefighters continued to battle a separate blaze in Montecito in Santa Barbara County. It was 40-per-cent contained Saturday evening. The cause is still under investigation.

That fire has forced the evacuation of more than 5,400 homes since it started Thursday night. More than 180 homes have been destroyed in the tony, star-studded community.

With files from the Associated Press