About 200 homes were destroyed in Yarnell and Glen Isla, about 85 miles from Phoenix, by a fast-moving fire sparked by lightning and fed by gusting winds and dry grass, according to the Arizona Republic.
The 19 victims were members of the Granite Mountain Hotshots, an experienced group of firefighters from Prescott, Arizona.
Officials lost radio contact with the crew at 4:30 PM, the Los Angeles Times cited Steve Skurja, assistant spokesman for the Yavapai County Sheriff's Office, as saying.
A helicopter crew spotted the bodies, he said.
All of the firefighters had deployed their emergency fire shelters — tent-like structures meant to shield a single occupant from flames and heat when there is no escape.
Skurja confirmed that 19 members of the 20-person crew had died. The sole survivor was hospitalized with injuries, but Skurja did not know the firefighter's condition.
"The fire was very aggressive. It just overtook them."
It was the deadliest wildfire involving firefighters in the US for at least 30 years, according to the Associated Press. It was also the highest death toll of firefighters in an incident since the Sept. 11 terrorist attacks on New York in 2001.
President Barack Obama described the men as "heroes" and said that the "thoughts and prayers" of all Americans would be with their families.
Prescott Fire Chief Dan Fraijo said:
"We grieve for the family. We grieve for the department. We grieve for the city. We're devastated. We just lost 19 of the finest people you’ll ever meet. These are the guys that will go out there with 40, 50 pounds of equipment. They'll sleep out there as they try to develop fire lines and put protection between homes and natural resources and still try to remain safe."