More than 350,000 homes in San Diego have been ordered evacuated after a dozen wildfires continued their relentless assault on Southern California, displacing more than a half million people, destroying hundreds of homes and businesses, and forcing federal officials to assist firefighting efforts.

Unless the shrieking Santa Ana winds subside, and that's not expected for at least another day, fire crews say they can do little more than try to wait it out and react — tamping out spot fires and chasing ribbons of airborne embers to keep new fires from flaring.

"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," said San Diego Fire Capt. Kirk Humphries. "We can save some stuff but we can't stop it."

Tentacles of unpredictable, shifting flame have burned across nearly 600 square miles, an area larger than New York City, killing two people, destroying more than 1,600 homes and prompting the biggest evacuation in California history, from north of Los Angeles, through San Diego to the Mexican border.

In San Diego County alone, 513,000 people have evacuated, said county spokesman Luis Monteagudo.

Fully a quarter of the California coast was ablaze. Flames climbed halfway toward the Nevada line, chewing through chunks of seven counties and devastating numerous communities.

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Hotter temperatures and more explosive Santa Ana gusts hampered the firefighting efforts, grounding helicopters and airplanes used to fight the blazes.

"We're just waiting for the winds to die down so those tankers can be used," Gov. Arnold Schwarzenegger said Tuesday, noting "there are homes being destroyed right now as we speak."

Earlier, Homeland Security Secretary Michael Chertoff inspected the conditions.

"We're facing at least another 24 hours of very bad conditions from the standpoint of firefighting and we're going to hope that we can ride that out and then be effective in responding to depress any further fire contagion," he said.

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Hundreds of federal firefighters from the Department of the Interior had been brought in to fight the fire, Chertoff said.

Across Southern California, more than 1,300 buildings have been destroyed. At least 346,000 homes were evacuated in San Diego County alone, sheriff's officials said. But the total number could be much higher, and state officials were still struggling to estimate how many people had fled.

Marilee Bishop of Running Springs and her 10-year-old daughter, Erica, rubbed their red eyes Tuesday morning as they woke up in a Wal-Mart parking lot where they spent the night after being forced to leave their home.

"No one ever expects something like this to happen to them," said Bishop, as thick smoke rose in the skies behind her.

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As the fires spread, most out of control, smaller blazes were merging into larger, more fearsome ones. Evacuations were being announced in one community after another as firefighters found themselves overwhelmed by gale-force Santa Ana winds, some gusting to 70 mph.

Authorities hadn't even begun to estimate the dollar value of the damage in some of the hardest-hit areas. A fire that struck Ramona, a city outside San Diego, had destroyed 650 structures. A blaze near Fallbrook, on the eastern edge of Camp Pendleton, wiped out another 500, or three buildings for every one firefighter allocated to it. And 200 more buildings burned in a fire just south of Potrero, across from the Mexican city of Tecate.

President Bush declared a federal emergency for seven counties, a move that will speed disaster-relief efforts. Bush will travel to California Thursday to get a close-up look at the devastation and emergency efforts.

"The president wants to travel to California to witness firsthand what the people there are going through with these wildfires," White House press secretary Dana Perino said. "He wants to ensure that the state and local governments are getting what they need from the federal government and he wants to make sure to deliver a message in person to the victims that he has them in his thoughts and prayers."

Bush and California Gov. Arnold Schwarzenegger agreed during a phone call that Thursday was the best day for a presidential visit.

"All of us across this nation are concerned for the families who have lost their homes and the many families who have been evacuated from their homes," Bush said Tuesday. "We send the help of the federal government."

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Fire crews and fleeing residents described desperate conditions that were sure to get worse. Temperatures across Southern California were about 10 degrees above average and were expected to approach 100 degrees Tuesday in Orange and San Diego counties.

Deputies arrested two men for looting in the community of Ramona, and there were a handful of other looting cases reported, said San Diego Sheriff's Lt. Mike McClain.

The fires were exploding and shooting embers in all directions, preventing crews from forming traditional fire lines and severely limiting aerial bombardment, officials said.

"Lifesaving is our priority. Getting people out from in front of the fire — those have been our priorities," said Capt. Don Camp, a spokesman for the California Department of Forestry and Fire Protection.

Thousands of residents sought shelter at fairgrounds, schools and community centers. The largest gathering was at Qualcomm Stadium in San Diego, where up to 10,000 evacuees anxiously watched the stadium's television sets, hoping for a glimpse of their neighborhood on the local news. San Diego Mayor Jerry Sanders pleaded for donations of blankets, cots, pillows and food for the people staying there, and officials said more people were expected to arrive Tuesday.

The wildfires claimed at least two lives. An unidentified civilian died of burns in a fire in Santa Clarita, in northern Los Angeles County, said U.S. Forest Service spokesman Jay Nichols. Another man, Thomas Varshock, 52, was found dead Sunday.

Overall, 45 people have been injured, 16 of them firefighters.

In San Diego County, public schools were closed, as were campuses at the University of California, San Diego and San Diego State University.

The scope of the infernos was immense and was reminiscent of the blazes that tore through Southern California four years ago this month, killing 22 and destroying 3,640 homes.

The fires have been made worse by fierce Santa Ana winds. The winds — which sweep through Southern California's canyons in fall and winter — are stronger than normal, turning already parched scrubland into tinder. They generated walls of flame that bore down on housing developments in a wide swath.

East of Los Angeles, a two-front fire destroyed at least 160 homes in the Lake Arrowhead area, the same mountain resort community where hundreds of homes were lost four years earlier. Officials said at least 100 more homes were destroyed Tuesday in the mountain community of Running Springs, not far away.

"It's just sad when you see that," Schwarzenegger said at a news conference after touring the area. "We have to do everything that we can to help these people ... to help them get back on their feet as quickly as possible."

The Associated Press contributed to this report.