At least 19 firefighters were killed Sunday battling a fast-moving wildfire in Arizona, officials said, in the deadliest incident of its kind in the United States in decades.
The firefighters died while racing to contain the Yarnell Hill wildfire north of Phoenix, in what Arizona governor Jan Brewer called "as dark a day as I can remember."
The deadly blaze came amid baking temperatures and tinder-dry conditions across the US southwest, with records broken over the weekend in Arizona and California, and follows an already deadly wildfire season across the region.
President Barack Obama paid tribute to those who lost their lives, in a statement issued while traveling in South Africa which lamented "this terrible tragedy."
"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."
The Yarnell Hill fire, believed to have been ignited by lightning, broke out Friday and according to local forestry officials has already covered 2,000 acres, spreading rapidly through the dry, forested area amid strong winds.
"It appears the firefighters had to deploy their fire shelters and were overcome by the fire," said an update on the Northeastern Arizona Public Information website, referring to last-ditch protection equipment.
Hundreds of residents of Yarnell and Peeples Valley were being evacuated, officials said on a fire alert website, as the blaze continued to tear through the area.
Prescott Fire Chief Dan Fraijo said he was "devastated" by the loss of lives.
"We just lost 19 of some of the finest people you will ever meet," he said at a press conference. "We take safety precautions, but sometimes, unfortunately, sometimes it just doesn't work out."
Figures from the National Fire Protection Association, a non-profit organization, show that the Arizona deaths are the worst firefighter fatalities from a wildfire since 29 firefighters died fighting a blaze in Los Angeles' Griffith Park in 1933.
Sunday's deaths also mark the largest loss of firefighter lives on US soil since the 9/11 attacks on the World Trade Center, when 340 firefighters were killed, according to NFPA statistics.
Federal help was set to arrive on Monday, local news site the Arizona Republic reported, but officials expected at least 250 homes -- about half the town of Yarnell -- would be destroyed by the inferno.
"This is as dark a day as I can remember," said Arizona governor Jan Brewer, as tributes poured in for the fallen firefighters.
Speaking to a local NBC affiliate, she added: "When we get these drought areas, sometimes it dries out, it just burns so quickly and so fast and tonight is another example of that.
"I guess it was a flash fire and it just turned around and it overcame them all. It was just one big swoop," she told KPNX-TV.
A state forestry official told CNN the firefighters, from a local "hotshot" crew, had been digging a fire line to contain the blaze.
"In normal circumstances, when you're digging fire line, you make sure you have a good escape route, and you have a safety zone set up," Art Morrison said.
"Evidently, their safety zone wasn't big enough, and the fire just overtook them."
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 blazes raging across the dry state and comes two weeks after a blaze in Colorado killed two people and burned down 360 homes, that western state'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 128 degrees.
The wildfire season flared up earlier than usual this year, with California, Arizona and New Mexico the hardest hit. As of Monday, there were over 40 active blazes in the three states, according to the inciweb fire information website.