A wind-whipped wildfire started by an arsonist killed four firefighters Thursday and stranded up to 400 people in an RV park when flames burned to the edge of the only road out, officials said.

"Everybody is hunkered down here. They're fighting the fire around us. It's across the street from us," said Charles Van Brunt, a ranger at the station at the entrance to Silent Valley Club, the recreational vehicle park near Palm Springs. The residents were in no immediate danger, he said.

Authorities asked people in the RV park to stay put to leave roads clear for firefighters. Hundreds of others in the area were forced from their homes.

Fire officials said the blaze was deliberately set around 1 a.m. Fire Chief John Hawkins said the arson "constitutes murder."

It was the deadliest wildfire firefighting disaster in the United States since July 10, 2001, when four firefighters were killed in Washington's Okanogan National Forest. They died after becoming trapped by flames on a dusty dead-end road in a remote canyon.

The Forest Service crew was trying to protect a house as dry desert winds of 25 mph or more blew a wall of flames down on them in the hills northwest of Palm Springs.

"They had left their truck to do structure protection when the fire overran them," said Forest Service spokesman Pat Boss, adding that the flames came down so quickly they had no time to retreat to their engine or use protective sheltering.

Three firefighters died at the scene, and two were hospitalized in critical condition. One of those two died several hours later. The other had burns over 95 percent of his body, Boss said.

The surviving firefighter had severe respiratory damage, said Dr. Dev Gnanadev, a trauma surgeon at Arrowhead Regional Medical Center.

"Overall, the chances of survival are low when you have that bad of an injury," he said at a news conference.

Thursday's deaths brought to 19 the number of California firefighters killed in the line of duty over the past year, according to statistics kept by California Professional Firefighters, a lobbying organization.

Boss said the Forest Service pulled all its personnel off the fire after the deaths so they could "gather their thoughts, say their prayers."

Another official believed the blaze was set just as the winds picked up in order to maximize destruction. Riverside County Sheriff Bob Doyle dispatched homicide detectives to the scene to work with FBI agents during the investigation.

Authorities planned to offer a $100,000 reward in the case.

"Turn that scum in, please," Riverside County Supervisor Marion Ashley said.

In less than 24 hours, the fire blackened almost 38 square miles, and more than 1,100 firefighters were brought in along with water-dropping helicopters and planes. Ten structures were destroyed, and at least five were homes.

The fire, which was only 5 percent contained, roared 15 miles to the west from where it began. Resources were being concentrated along a highway that firefighters hoped to keep the blaze from crossing.

"We're going to be here, and we're going to hit it hard," Hawkins said.

The weather service had issued a "red flag" warning for extreme fire danger because of the high winds and dry conditions.

Thick smoke blanketed the small RV park, where as many as 400 people were stranded for hours, authorities said. TV footage showed some vehicles racing through flames and smoke just before firefighters closed the road.

Van Brunt said people were advised to "watch the news and stay comfy."

The fire was stymied by a firebreak created around Poppet Flat and the RV park years earlier, sheriff's Cpl. Todd Garvin said.

"This is a safe haven here. That was cleared about six years ago and it still works. It's amazing," Garvin said.

Some residents of Poppet Flat sought shelter at the RV park, officials said.

The fire burned in a valley with a few scattered ranch homes. The hamlets of Poppet Ranch and Twin Pines were evacuated along with a juvenile detention center, Twin Pines Boys Ranch.

In all, nearly 700 people were evacuated, Gov. Arnold Schwarzenegger told reporters in Sacramento. Schwarzenegger signed an emergency proclamation designed to free up state resources to help fight the blaze and make Riverside County eligible for financial assistance.

Construction contractor Charlie Miner suffered minor burns when he drove his backhoe through the flames to escape in Twin Pines. "It was so intense I was screaming," Miner said. "Sparks were flying everywhere."

The firefighters who were killed were members of a five-person crew based in the nearby town of Idyllwild, Boss said.

He said late Thursday that his friend, Capt. Mark Loutzenhiser of Idyllwild, was among the victims.

"It's not past tense. Mark's still a wonderful person — no matter where he is, where he's lying or who he's with right now — he's still a great person in my eyes," a tearful Boss told KCAL-TV. The names of the other firefighters were not immediately released.

As news of the deaths spread, friends stopped at the Idyllwild ranger station to express their sympathies.

"You guys are our saving grace," said Emily Pearson, as she hugged Boss. "It shouldn't have happened." Pearson said she had lived in the area 35 years, and her family knew all five firefighters.

The strong winds fed the blaze oxygen and dried out the region's already parched vegetation, Hawkins said.

The fire could be seen burning along ridgelines, with flames leaping as high as 100 feet into the air. Pillars of smoke were quickly blown away, and at one point, smoke could be smelled on the Pacific coast, 100 miles away.

Timo Hargu, 61, said he rushed from his hilltop home with his two dogs after he looked out a window and saw fire burning toward him in a valley.

"The whole thing was ablaze with flame," he said. "It was the most spectacular view. A terrible view, but spectacular."

By nightfall the fire's main front was pushing west toward Lambs Canyon, a sparsely populated, rugged area with brush several feet high, said Diana Newcomb, a spokeswoman for the California Department of Forestry.

Residents of Poppet Flat were told they could leave the RV park and go home. Visitors who came in RVs were told to stay put because firefighters did not want motor homes clogging the road.