PRESCOTT, Arizona (AFP) - Reinforcements poured in Monday to battle a runaway wildfire in Arizona that quadrupled in size overnight after killing 19 firefighters in one of the worst such incidents in US history.
The Yarnell Hill fire - which killed all but one member of a 20-strong "hotshot" team - caused the biggest loss of life among firefighters since the Sept 11 attacks, and the most from a US wildfire in 80 years.
As a make-shift memorial grew outside the dead firefighters' 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.
"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 honour 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."
The raging fire has ripped through more than 3,200ha some 135km north of Phoenix, 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."
"Until we get a significant showing of the monsoons, it's show time and it's dangerous, really dangerous," added incident commander Roy Hall.
The dead firefighters' names were not immediately released by authorities, but 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 Ms Ashcraft, who learned about the tragedy while watching TV with her four children.
Another of the victims was named as Kevin Woyjeck, 21, the son of a Los Angeles County Fire Department (LACFD) captain, according to LACFD inspector Tony Aikens.
The US south-west has seen soaring temperatures, with records broken over the weekend in Arizona and California, and this year's wildfire season had already proved deadly elsewhere in the tinder-dry region.
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.
Federal help was set to arrive on Monday, local news site the Arizona Republic reported, but officials expected that at least 250 homes - about half the town of Yarnell - would be destroyed by the inferno.
A Facebook page has been created in memory of the fallen firefighters, showing a picture of the Granite Mountain Hotshots crew from Prescott, Arizona, with 19 people in the photo.
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 53 deg C.