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The Prescott fire chief said his organisation and city were in grief after 19 firefighters from his department died in the wildfire blaze.
Arizona Governor Jan Brewer said the tragedy was "as dark a day" as she could remember.
- An elite team of 19 firefighters have been killed in the Arizona wildfire.
- There have only been seven previous incidents in the last century that has seen as many or more firefighters killed, topped by the loss of 340 during the September 11 attacks.
- Two towns, which lie southwest of Prescott, Arizona, have been evacuated.
- Around 1,000 people live in the evacuated Yarnell and the adjoining town of Peeples Valley.
- At least 200 structures, mainly houses, have been destroyed by the wildfire.
- The blaze has charred more than 2,000 acres of land.
US President Barack Obama said the 19 firefighters killed in the Arizona wildfire blaze were "heroes" who "selflessly put themselves in harm's way" to protect fellow citizens.
He said: "Yesterday, nineteen firefighters were killed in the line of duty while fighting a wildfire outside Yarnell, Arizona.
"They were heroes - highly-skilled professionals who, like so many across our country do every day, selflessly put themselves in harm's way to protect the lives and property of fellow citizens they would never meet.
"In recent days, hundreds of firefighters have battled extremely dangerous blazes across Arizona and the Southwest. The federal government is already assisting, and we will remain in close contact with state and local officials to provide the support they need.
"But today, Michelle and I join all Americans in sending our thoughts and prayers to the families of these brave firefighters and all whose lives have been upended by this terrible tragedy."
Nineteen firefighters from an elite team were killed in the Arizona wildfire that has destroyed around 200 houses and forced the evacuation of two small towns near state capital Phoenix.
The tragedy ranked as the greatest loss of life among firefighters from a single wildfire blaze in the US in 80 years, since 29 men were killed battling the Griffith Park fire of 1933 in Los Angeles.
Art Morrison, from the Arizona State Forestry Commission, told CNN the firefighters, who were members of a specially trained "hot shot" team, were killed when they were overtaken by the fast-moving flames.
He said: "In normal circumstances, when you're digging fire lines, you make sure you have a good escape route, and you have a safety zone set up. Evidently, their safety zone wasn't big enough, and the fire just overtook them. By the time the other firefighters got in, they didn't survive."
Prescott Fire Chief Dan Fraijo called the tragedy "one of the worst wildfire disasters that's ever taken place."
He added that one member of the 20-man crew happened to be in a separate location and survived. There was no immediate information on his condition.
A wildfire sweeping through Arizona that has killed 19 firefighters has also destroyed around 200 houses, according to the Associated Press.
Very high temperatures, low humidity and strong winds have combined to create a fierce wildfire in the US state of Arizona.
Officials have ordered the evacuations of more than 50 homes in several communities as firefighters try to control the blaze.
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Firefighters have been working to bring a wildfire under control close to the US town of Yarnell, about 90 miles north-west of Pheonix, Arizona.
The local press is reporting that state authorities plan to call in federal help to battle the 2,000-acre blaze.
About 200 firefighters are working to control the blaze, which has destroyed several homes in the community.
Nineteen firefighters were killed battling a fast-moving wildfire menacing a small town in central Arizona, the US Wildland Fire Aviation service said on Sunday.
The firefighters died fighting the Yarnell Hill Fire, near the small town of Yarnell about 80 miles (128km) northwest of Phoenix, the service said in a Facebook post.
The fire has charred about 1,000 acres (405 hectares) of chapparral and grass since Friday amid tinder-dry heat wave conditions, leading to scores of evacuations near Yarnell.
Cooling stations have been set up to shelter the homeless and elderly people who cannot afford to run their air conditioners, as a potentially dangerous heatwave blistered parts of western US.
In California, Nevada and Arizona, air-conditioned "cooling centres" were set up in community centres, homeless shelters and libraries, and officials warned residents to avoid prolonged exposure to the searing temperatures.
In Phoenix, emergency shelters are temporarily adding 150 beds in an effort to safeguard hundreds of homeless.
An 'excessive heat warning' for "potentially life-threatening" heat, has been issued by the US National Weather Service as a heatwave blistered western parts of the country.
The agency said on their website: "Excessive heat warnings remain in effect for a large portion of California...Nevada...and Arizona...where daytime highs will yet again dangerously soar well past the century mark and overnight lows will barely drop into the seventies and eighties.
"The south west will be particular hot with several places exceeding 110 degrees. One of the hottest places will be Death Valley, California as temperatures will approach 130 degrees".