LOS ANGELES: An aggressive wildfire in Southern California seared its way through dry vegetation Friday and spread quickly, destroying more than a dozen homes as tens of thousands of residents were ordered to get out of its way, authorities said.

The blaze broke out Thursday evening in the San Fernando Valley and spread westward, burning its way into hilly subdivisions on the northern edge of Los Angeles as terrified residents grabbed what they could and ran. One man went into cardiac arrest and died, authorities said.

Those who left included Edwin Bernard, who said he never saw the flames arrive so quickly or come so close to his home as this time.

He watched as the fire swept down a hillside, sizzling through dry grass and igniting trees and bushes and spitting embers over his home of 30 years. He and his wife fled in their car, leaving behind medication, photo albums and their four cats.

"It was a whole curtain of fire," Bernard said Friday. "There was fire on all sides. We had to leave."

The region has been on high alert as notoriously powerful Santa Ana winds brought dry desert air to a desiccated landscape that only needed a spark to erupt.

The Los Angeles fire broke out hours after flaming garbage in a trash truck sparked another blaze when the driver dumped his load to keep the rig from catching fire. But the dry grass quickly ignited and powerful winds blew the flames into a mobile park in Calimesa, about 75 miles (120 kilometres) east of downtown Los Angeles. About three-quarters of the 110 homes were wiped out and one resident died, fire officials said.

The two fires burned as power was restored to most of the nearly 2 million residents in the northern part of the state who lost electricity after Pacific Gas & Electric Co switched it off Wednesday to prevent a repeat of the past two years when its equipment sparked deadly, destructive wildfires during windy weather.

Officials had worried that gusts might topple trees on and blow other vegetation into transmission lines and start wildfires, but the move was widely criticized for targeting areas that faced no danger, and for disrupting so many lives.

The family initially blamed the outage for the death of an El Dorado County man dependent on oxygen, but the coroner later said he died from severe coronary disease.

The Los Angeles fire erupted in the neighbourhood of Sylmar in a giant plume of red glowing smoke that expanded rapidly and could be seen for miles. It spread westward at a rate of 800 acres (324 hectares) an hour into Granada Hills and Porter Ranch, where subdivisions crowd against the foothills of the Santa Susana Mountains. About 100,000 people in over 20,000 homes were ordered to evacuate, Los Angeles Police Chief Michel Moore said.

Its cause wasn't immediately known, though arson investigators said a witness reported seeing sparks or flames coming from a power line near where the fire is believed to have started, said Peter Sanders, a spokesman for the Los Angeles Fire Department.

At least two people told LA TV stations that they saw fire near power lines around the time the blaze broke out.

Southern California Edison said it owns the transmission tower shown on KABC-TV, but a spokeswoman would not confirm that was where the fire began. The utility said it could take a long time to determine the cause and origin of the fire.

Porter Ranch, an upper-middle-class suburb that was the backdrop for the 1982 movie "ET" is no stranger to evacuations. Four years ago, a blowout at a nearby underground natural gas well drove 8,000 families from their homes for more than 100 days. The community also sits next to Northridge, which was the epicentre of a rattling earthquake 25 years ago.

By Friday, the fire had grown to more than 11 square miles (29 sq kilometres) and at least 31 homes were damaged, Fire Chief Ralph Terrazas said. A middle-aged man who was near the fire went into cardiac arrest and died, the chief said, but he did not have details.

Flames roared through dense chaparral on steep hillsides and thick smoke blanketed parts of the valley. Some areas were sunny with blue skies and others were obscured in a grey haze. The air quality was so poor in some places that shoppers in Canoga Park wore breathing masks.

Schools and colleges closed for the day and Interstate 5, the main north-to-south corridor in the state, was shut down at the northern end of Los Angeles. Several sections of nearby freeways were also closed for much of the day.

More than 1,000 firefighters were deployed to corral the blaze. Helicopters, planes and jumbo jets swooped low over neighbourhoods to drop water on flames and spread red retardant across ridges to give firefighters on the ground a chance to halt the fire's advance amid strong winds.

"As you can imagine the embers from the wind have been travelling a significant distance which causes another fire to start," Terrazas said.

Jonathan Stahl was driving home to Valencia when he saw the smoke and immediately diverted to a mobile home park in Sylmar where his grandmother and aunt live together.

The park had been nearly wiped out in 2008 when one of the city's most destructive fires levelled 500 homes.

"Oh my God, it's coming this way," his aunt said when Stahl called to alert them and she looked out the window, he said.

Stahl helped his grandmother, Beverly Stahl, 91, who was in her pyjamas, and his aunt to pack clothing, medication and take their two dogs. They saw flames in the distance as they drove away.

"We just packed up what we could as fast as we could," Stahl said at an evacuation centre at the Sylmar Recreation Center, massaging his grandmother's shoulders as she sat in a wheelchair with a Red Cross blanket on her lap. "If we'd stuck around, we would have been in trouble. Real big trouble."

At the site of the other fire, in Calimesa, residents of the trailer park anxiously waited to see if their homes had survived the fast-moving blaze.

Seventy-four buildings were destroyed and 16 others were damaged. Several people were injured, Cal Fire spokeswoman Cathey Mattingly said.

One worried resident said he couldn't reach his 89-year-old mother after she called to tell him she was evacuating.

"She said she's getting her purse and she's getting out, and the line went dead," Don Turner said.

He said neighbours saw his mother, Lois Arvickson, in her garage as flames approached and later saw the garage on fire, but they didn't know if she'd managed to escape.

Melissa Brown said she moved to the mobile home complex earlier this year from Arizona, in part to help take care of her mother who has since died. Brown said she now also faces the loss of her home.

"The hardest part is my mom's remains are in there," she said Friday morning, choking back tears.