The bodies of 19 young firefighters killed in America's deadliest wildfire in 80 years were removed in a cortege of white vans, as experts probed how they perished so suddenly.

The names of the dead men, mostly in their 20s, were released a day after the Yarnell Hill fire tragedy, in which all but one of a 20-strong elite team were killed, many in cocoon-like last-ditch protection shelters.

The blaze, which quadrupled in size overnight, was the most lethal since September 11, 2001, which cost the lives of 340 firefighters in the ashes of the Twin Towers in New York.

As a makeshift memorial grew outside the victims' home station, including American flags and 19 water bottles arranged in a heart shape, Arizona governor Jan Brewer ordered flags to be flown at half-staff through Wednesday.

"The Yarnell fire exploded into a firestorm that overran the local Granite Mountain hotshots," she said, using the name of the elite firefighting unit, which typically goes in first to set up initial fire containment lines.

Recalling the 340 who died on 9/11, she added: "Just as we honor the memory of the firefighters lost that day as they charged into the burning towers, we will remember the brave men of the Granite Mountain hotshots."

President Barack Obama telephoned Brewer -- a Republican with whom he has previously had strained relations -- to pledge federal aid to help learn from the tragedy, and deal with the blaze.

"He also expressed his gratitude to the hundreds of first responders who continue to work around the clock to protect homes and businesses from this deadly blaze," the White House said in a statement.

The victims' bodies were loaded into a fleet of white coroner's vans Monday for the 85 mile (135 km) trip south to Phoenix, where a large stars-and-stripes flag billowed in the wind as they arrived, guards standing solemnly by.

By Monday the raging fire had ripped through more than 8,000 acres (3,200 hectares), up from 2,000 late Sunday, and was zero percent contained, officials said.

High winds were expected to worsen the blaze, complicating the task for the some 400 firefighters now battling it, up from 200 on Sunday.

"It's a very difficult situation," said Arizona land management spokesman Dennis Godfrey. "The high winds are a real danger... It's even a greater danger when those winds are shifting directions."

The dead firefighters' names were released: 14 of them were in their 20s; the youngest was 21, the oldest 43. Officials stressed that the nature of the hotshots' work meant they needed to be in the peak of physical fitness.

Juliann Ashcraft told the AZ Central website that her husband Andrew died in the blaze.

"They died heroes .. We'll miss them. We love them," said Ashcraft, who learned about the tragedy while watching TV with her four children.

Officials said the deaths were under investigation but that the firefighters appeared to have deployed fire shelters -- last-ditch protection equipment -- just before they were engulfed in flames.

"It's a very elite group of people who are highly trained, highly motivated, very fit... We don't know what happened," Wade Ward, a visibly shocked Prescott Fire Department spokesman, told CNN early Monday.

Hundreds of residents of Yarnell and Peeples Valley were meanwhile evacuated, officials said, as the blaze continued to tear through the area.

Figures from the National Fire Protection Association (NFPA) show that the Arizona deaths are the worst firefighter fatalities from a wildfire since 29 died fighting a blaze in Los Angeles's Griffith Park in 1933.

The Yarnell Hill wildfire is the worst of several raging across Arizona and comes two weeks after two people died and 360 homes burned down in the western state of Colorado's most destructive blaze ever.

Record and near-record temperatures left much of the US southwest sweltering over the weekend, with Death Valley in California equaling the hottest ever June temperature in the United States, at 129 degrees Fahrenheit (53 Celsius).