Dying winds gave California firefighters their first big break on Wednesday after four days battling wildfires, but San Diego faced more calamity as blazes there burned out of control and kept more than half a million evacuees from returning home.

The skies over much of the region were filled with thick, acrid smoke, forcing residents to stay indoors or wear masks.

California Gov. Arnold Schwarzenegger said 18 fires burned on Wednesday and threatened 25,000 structures. Nearly 1,500 homes had already been lost. San Diego bore the brunt of the damage and officials there put losses in excess of $1 billion.

More than 500,000 people have been forced to leave their homes in the biggest mass evacuation in California's modern history.

Six deaths have been reported, while 40 people suffered injuries, many of them firefighters.

Two big fires merged in San Diego County, scorching more than 200,000 acres, almost half of the total burned area in California.

"We have several tremendous fires still going on," San Diego Mayor Jerry Sanders said.

Los Angeles County canceled its wind warnings four days after hot Santa Ana winds blew in from the desert and sparked the first fire in the seaside celebrity enclave of Malibu, where life had begun returning to normal by Wednesday.

Mountain blazes east of Los Angeles were the worst, but firefighters said calmer wind conditions would make a big difference. Top wind speeds fell to below 50 mph (80 kph) after gale force gusts hit 80 mph (130 kph).

Schwarzenegger said 8,900 firefighters remained on the fire lines.

BUSH DECLARES DISASTER

"A lot of them have worked 36 hours and 48 hours without stopping," Schwarzenegger said.

President George W. Bush on Wednesday declared a "major disaster" in seven Southern California counties, triggering extra federal help. He will travel to the region on Thursday to get a close-up look at the devastation.

San Diego, state and federal authorities set up food, shelter and medical services for the displaced, amid sharp memories of the debacle following Hurricane Katrina in New Orleans.

At San Diego's Qualcomm Stadium, where the National Football League's San Diego Chargers play, 14,000 evacuees spent a second night.

But evacuees said they were pleased with the official response to their needs, the clean conditions, abundant food and water and even yoga, acupuncture and massage.

Even animals were being accommodated, with evacuated horses put up at the county fairgrounds.

Some residents were allowed to go back to their homes, but officials kept many waiting while they dealt with hot spots.

"I have a place to go home to. I know because my answering machine is still working, which means it's not melted," said Helle Powell, 61, a resident of Rancho Bernardo, one of the worst-hit areas.

San Diego County officials said that even when the fires were out they would face a major cleanup and huge costs.

"Based on initial estimates, just the homes damaged will be over $1 billion," Ron Lane, San Diego County emergency services director, told a news conference.

San Diego told residents to conserve water and electricity, as the fires sliced power supply to 60 percent of normal and threatened to cut off the area from the state's power grid.

Sanders implored residents to cut power use, telling them: "You've got to conserve today. You have no choice."

A nuclear power plant in San Onofre was not in immediate danger, officials said, despite fires burning at the nearby Marine base of Camp Pendleton, one of the largest military bases in the United States.

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