More than 1,000 firefighters and nine water-dropping aircraft battled the 4,700-acre Marek Fire at the northeast end of the San Fernando Valley, and the 5,000-acre Sesnon Fire at the west end.
Winds blew up to 45 mph with gusts reaching 70 mph at midday. They were forecast to diminish in the evening before roaring over 60 mph after 11 p.m.
"This fire has the real potential of moving from where it is now ... as far as Pacific Coast (Highway)," said Los Angeles County Fire Chief P. Michael Freeman.
Residents downwind were warned to remain alert into the night. "It can go from here to the ocean in a matter of two to three hours," said Los Angeles County Supervisor Zev Yaroslavsky.
Authorities confirmed more than three-dozen mobile homes burned at the Marek Fire and TV news helicopter crews counted about 10 homes destroyed by the Sesnon Fire. More than 15 square miles were charred by both flames combined.
"It is a blowtorch we can't get in front of," said Los Angeles County fire Inspector Frank Garrido.
Fire officials alerted other communities to the west in the Ventura County city of Simi Valley and south to Malibu, 20 miles away, as an ominous plume streamed over neighborhoods and far out to sea.
Residents were not allowed to drive into one of Porter Ranch's gated communities because officials wanted to keep roads clear for emergency vehicles. Instead they parked their cars, ran to their homes and carried out whatever they could carry in pillow cases, in their arms, sacks and suitcases. Some ran out clutching paintings.
Freeman warned people not to stay home after evacuation orders had been given. "You may not be able to even outrun this fire," he said.
A man was killed in four-vehicle crash on the nearby 118 Freeway. California Highway Patrol Officer Leland Tang said traffic had stopped because firefighters were going by as fire neared the route. At some point, motorists stopped on the freeway because of the flames and CHP officers turned them around to use an on-ramp as an exit, said CHP Capt. J.D. Goodwin.
Earlier, a fatality was discovered at the Marek Fire, an area where neighborhoods abut rugged canyonlands below the mountainous Angeles National forest. The man appeared to have been a transient living in a makeshift shelter, officials said.
About 1,200 people evacuated due to the Marek Fire, which was just 5 percent contained.
"We could have had an army there and it would not have stopped it," Los Angeles Fire Department Battalion Chief Mario Rueda said. "Wind is king here, it's dictating everything we are doing."
Mobile home park resident Glenn Bell said he and another park resident broke a padlock on an emergency exit gate to escape at daybreak. "If we hadn't broke open that gate, there would be people dead up there," he said.
Olive View-UCLA Medical Center moved five of its most fragile patients to other hospitals. Spokeswoman Carla Nino said the four newborns and the fifth patient were on ventilators and were the most difficult to transport. Some other patients were discharged but the hospital decided it was not necessary to evacuate about 180 others.
The dry and warm Santa Ana winds typically blow between October and February. As they whistle through Southern California canyons and valleys, they accelerate, drying out vegetation and hastening the spread of any fires that erupt.
"This is what we feared the most," Los Angeles County fire Capt. Mark Savage said. "The winds that were expected - they have arrived."
Flames jumped the Foothill Freeway, which was closed in both directions for about a three-mile stretch in northern Los Angeles between the 118 Freeway and Interstate 5 amid the morning rush hour, officials said.
"That was quite a jump. That's an eight-lane fire break," said fire spokesman Inspector Paul Hartwell.
The South Coast Air Quality Management District advised Monday that air quality may be unhealthful due to the fires and urged people to avoid outdoor activities.
The Red Cross said about 500 people registered at an evacuation center at San Fernando High School. Agency spokesman Nick Samaniego said some evacuees had seen news footage of their homes burning.
"You can imagine, it's a devastating situation," he said. "A lot of people on pins and needles waiting to hear news about their communities."
Most schools in the area were closed Monday.
In San Diego County, a wildfire that began on an explosives training range at Camp Pendleton forced the evacuation of a military housing area and 100 nearby homes in Oceanside.
Firefighters also contained smaller blazes elsewhere in southern California.
In northern California, a blaze charred more than half of Angel Island in San Francisco Bay, but spared historical structures on the island, including an immigration station that was the first stop for millions of immigrants, mostly from China, in the early 1900s.
Associated Press writers Greg Risling, Thomas Watkins, Alicia Chang, Christina Hoag and John Rogers contributed to this report.