Firefighters struggled to contain a runaway wildfire in the US state of Arizona Monday after 19 of their comrades were killed in one of the worst such incidents in US history and two towns were evacuated.
The firefighters died while racing to contain the Yarnell Hill wildfire about 135 kilometres 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 travelling 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 and fanned by high winds, broke out Friday and has swept across 2,000 acres, spreading rapidly through the dry, forested area.
Officials said that the incident was 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 not reality for us, it hasn't really set in," Wade Ward, a visibly shocked Prescott Fire Department spokesman, told CNN early Monday.
"It's a very elite group of people who are highly trained, highly motivated, very fit... We don't know what happened."
Hundreds of residents of Yarnell and Peeples Valley were meanwhile evacuated, officials said on a fire alert website, as the blaze continued to tear through the area.
Figures from the National Fire Protection Association, a non-profit organisation, 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.
Record and near-record temperatures left much of the US southwest sweltering over the weekend, with Death Valley in California equalling the hottest ever June temperature in the United States, at 53 Celsius.
As of Monday, there were over 40 active blazes in the four states, according to the inciweb fire information website.