By Holly Yan, CNN
(CNN) -- They were part of an elite squad who confronted wildfires up close, setting up barriers to stop their destructive spread.
But the inferno blazing across central Arizona proved too much.
The 19 firefighters were killed Sunday while fighting the Yarnell Hill fire, northwest of Phoenix. It is the deadliest blaze for firefighters since the 9/11 attacks.
"Our entire crew was lost," Prescott Fire Chief Dan Fraijo told reporters Sunday night. "We just lost 19 of some of the finest people you'll ever meet. Right now, we're in crisis."
The tragedy decimated the Prescott Fire Department by about 20%. Fraijo said one member of the team was not with the other crew members and survived.
Authorities believe lightning sparked the Yarnell Hill fire on Friday. By Sunday night, it had scorched more than 6,000 acres and destroyed more than 100 structures, incident commander Mike Reichling said.
Billows of thick black smoke covered the sky as the whopping flames leaped from one stretch of parched land to another.
The wildfire also forced evacuations in Peeples Valley and Yarnell, but no civilian injuries were reported.
Drivers fleeing the area were chased by dark plumes filling the air. Some evacuees paused from afar, wondering if the flames had torched their homes.
'The elite firefighters'
The blaze hadn't touched Prescott yet. But like many other fire departments across the state, the Prescott team jumped in to help.
The firefighters were members of a "hotshot" crew, tasked with digging a firebreak and creating an escape route.
"A hotshot crew are the elite firefighters," state forestry spokesman Art Morrison said. "They're usually (a) 20-person crew, and they're the ones who actually go in and dig the fire line, cut the brush to make a fuel break. And so they would be as close to the fire as they felt they safely could."
"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," Morrison said. "Evidently, their safety zone wasn't big enough, and the fire just overtook them."
Fraijo, the fire chief, said he did not know the exact circumstances surrounding the firefighters' deaths and wouldn't speculate on a cause. But he said drought conditions, combined with winds that whipped unpredictably, have made battling the flames especially difficult.
'They were heroes'
President Barack Obama lauded the efforts of the fallen firefighters.
"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," he said in a statement.
Arizona Gov. Jan Brewer, who will visit Prescott on Monday, said the loss marked "as dark a day as I can remember."
"It may be days or longer before an investigation reveals how this tragedy occurred, but the essence we already know in our hearts: fighting fires is dangerous work," she said.
"When a tragedy like this strikes, all we can do is offer our eternal gratitude to the fallen, and prayers for the families and friends left behind."
Fraijo said the firefighters who died were exceptionally dedicated to their jobs.
"These are the guys that will go out there with 40, 50 pounds of equipment and walk five miles. They'll sleep out there as they try to develop fire lines" to protect homes, Fraijo said.
Before the 19 deaths in Arizona, 43 firefighters had been killed so far in 2013, according to the U.S. Fire Administration. A total of 83 firefighters died last year while on duty.
A Facebook page in memory of the Arizona firefighters garnered more than 120,000 "likes" in less than 10 hours.
"Such a tragic loss," one person wrote. "My heart aches for these brave souls, and for their families and friends."
CNN's Janet DiGiacomo, Ric Ward, Dave Alsup and Marlena Baldacci contributed to this report.