Arizona State Forestry Division fire-prevention officer Carrie Dennett said the inferno -- fast-moving and erratic in its behavior -- was abetted by low humidity, high temperatures and extremely dry, dense fuel, and the Granite Mountain Interagency Hotshot Crew was trapped between two ridges when the wind suddenly changed direction, The Arizona Republic reported.
The elite firefighters may not have established an adequate escape route, a state forestry spokesman said.
Although state Forestry Division spokesman Mike Reichling told the Republic Monday standard procedures were followed, forestry spokesman Art Morrison said the firefighters had not established a route to a safe site large enough for all 20 members of the team, the Los Angeles Times reported.
Morrison said the fact that search teams found the firefighters' bodies in or near their emergency fire shelters suggests they were overrun by the flames.
"Obviously it wasn't a big enough open field ... if they had to deploy their shelters," Art Morrison said.
"They were too close to heavy fuels, so they got overrun," he said.
The high-tech, tent-like fire shelters are the last line of defense for front-line firefighters, to protect themselves from the roaring flames, state fire officials said.
The fire, which has destroyed more than 200 homes, raged out of control Tuesday, growing to more than 9,000 acres.
The Republic Tuesday quoted Incident Commander Clay Templin as saying the fire was 8 percent contained, with full containment expected by July 12.
More than 400 firefighters were battling the blaze. The Yavapai County Sheriff's Office Monday directed people living in Yarnell and Peeples Valley to evacuate their homes.
Karen Takai, a spokeswoman for the firefighting operation, told reporters at a news conference Tuesday teams fighting the wildfire "have to acknowledge" the loss of the Granite Mountain Hotshots but must not let it distract them from the job at hand.
"You can't push it behind in your head, but acknowledge it, and then they get their head back in the game," she said. "They have to focus very hard on the ground, or we'll be in that same circumstance again."
The U.S. Forest Service took command of the fire from state forestry officials late Monday, making the fire a "Type 1" incident, which will bring in the most experienced teams and potentially more resources, the Republic said.
The U.S. military is deploying four specially equipped C-130 firefighting aircraft to help fight the Yarnell Hill fire, CNN reported.
Arizona Gov. Jan Brewer declared a state of emergency and ordered flags across the state lowered to half-staff.
"I am so sorry we come together today under these very tragic circumstances," Brewer told reporters in Prescott, 35 miles northwest of the tiny town of Yarnell, where the men were killed by an epic wildfire stoked by unpredictable, gusty winds, triple-digit temperatures and low humidity.
The weather was forecast to be more of the same Tuesday.
Brewer said the Yarnell Hill fire, about 80 miles northwest of Phoenix, had exploded into a "firestorm" that overcame even the most experienced firefighters.
The tragedy "will forever ring as one of our state's darkest, most devastating days," Brewer said in a statement.
"It will forever remind us of the constant peril our firefighters selflessly face protecting us," she said. "We can never repay these nineteen men and their families for their service and the ultimate sacrifice they made on our behalf. We can, however, offer them our deepest, eternal debt of gratitude."
President Barack Obama, traveling in Africa, said the firefighters "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 deaths were the largest firefighting loss of life in Arizona history and the worst U.S. wildland firefighting tragedy since 29 firefighters were killed in the 1933 Griffith Park fire in Los Angeles.
Sunday's deaths were the largest fire department loss of life since the Sept. 11, 2001, terrorist attacks.
White vans carrying the fallen firefighters' remains drove from Yarnell to Phoenix, where they passed beneath American flags hanging from two giant ladder trucks.
The firefighting crew included four rookies, Prescott Fire Chief Dan Fraijo told reporters.
Fourteen of the dead were in their 20s, he said. The youngest were 21.
The fire wiped out a crack fire brigade that had been in development for 20 years, he said. "There's no one left."
One hotshot was away from the group at the time.