More than 500,000 people were forced to evacuate as wildfires raged for a third day across Southern California. At least 1,300 homes have been destroyed.

Earlier reports had said two people died because of the fires, but that was later lowered to one. More than 50 people have been injured, at least 18 of them firefighters desperately trying to save homes.

The wildfires are driven by the hot, dry Santa Ana desert winds, which are unlikely to fade for at least another day.

"If it's this big and blowing with as much wind as it's got, it'll go all the way to the Ocean before it stops," San Diego Fire Capt. Kirk Humphries told The Associated Press. "We can save some stuff but we can't stop it."

Tuesday saw even hotter temperatures and more explosive gusts of wind since the weekend, prompting one of the biggest evacuations in the state's history ranging from the Mexican border in the south, through San Diego to Los Angeles in the north.

"Currently we have 15 fires burning in seven counties in the Southern California region," Michael Sicilia, of the Emergency Services Office, told CTV Newsnet from Mather, Calif.

Gov. Arnold Schwarzenegger said the flames were threatening 68,000 more homes.

"We have had an unfortunate situation that we've had three things come together: very dry areas, very hot weather and then a lot of wind," he said Tuesday afternoon in a press conference. "And so this makes the perfect storm for a fire."

Earlier Tuesday, U.S. President George Bush declared a federal state of emergency in the region. The move is aimed at speeding up delivery of federal disaster relief to firefighters.

A White House statement said Tuesday's emergency declaration authorizes Homeland Security and the Federal Emergency Measures Agency (FEMA) to co-ordinate disaster relief efforts in the counties of Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, and Ventura.

In Rancho Santa Fe, a suburb north of San Diego, houses burned just yards from where fire crews fought to contain flames engulfing other properties. In the mountain community of Lake Arrowhead, cabins and vacation homes went up in flames with no fire crews in sight.

As dawn broke, authorities ordered new mandatory evacuations for residents in parts of San Diego County. Residents in about 3,800 homes in Wildcat Canyon and Multh Valley were told to evacuate. So were residents in another 1,800 homes in North Jamul and Indian Springs.

State officials said Tuesday that evacuee estimates could rise as officials are still working on the figures.

Sheriff's officials say at least 513,000 homes have been ordered evacuated in San Diego County alone. At least 600 buildings, including 500 homes and 100 commercial properties, have been destroyed in northern San Diego County.

San Diego's Qualcomm Stadium, home to the NFL's Chargers, was turned into an evacuation centre, where thousands of people huddled and watched TV reports on the disaster.

In Orange County, heavy smoke forced officials to evacuate more than a thousand inmates from a jail and bus the prisoners to another facility in Irvine.

One of the fires, in Orange County, is believed to have been set by arsonists. Other blazes, threatening the homes of celebrity-laden Malibu, are believed to have been caused by power lines.

Among the celebrities forced to flee were Mel Gibson, Kelsey Grammer and Victoria Principal, their publicists confirmed.

With files from The Associated Press