Arizona is in the midst of a historic drought that has left large parts of the state highly flammable.
"Until we get a significant showing of the monsoons, it's show time and it's dangerous, really dangerous," incident commander Roy Hall said.
Television aerial video footage showed law enforcement vehicles patrolling Yarnell, driving streets with burned buildings on both sides.
The National Fire Protection Association website lists the last wildland fire to kill more firefighters as the 1933 Griffith Park fire of Los Angeles, which killed 29. The biggest loss of firefighters in U.S. history was 343, killed in the 9/11 terrorist attack in New York.
Prescott, which is more than 30 miles northeast of Yarnell, is home to one of 110 hotshot crews in the United States, according to the U.S. Forest Service website. The unit was established in 2002.
In 1994, the Storm King Fire near Glenwood Springs, Colo., killed 14 firefighters who were overtaken by a sudden explosion of flames.
President Barack Obama called the 19 people heroes and said in a statement that the federal government was assisting state and local officials.
As the blaze spread, people started fleeing, including Chuck Overmyer and his wife, Ninabill. They were helping friends leave when the blaze switched directions and moved toward his property. They loaded up what belongings they could, including three dogs and a 1930 hot rod, on a trailer.
As he looked out his rear-view mirror he could see embers on the roof of his garage.
"We knew it was gone," he said.
He later went to the Arrowhead Bar and Grill in nearby Congress, where he and other locals watched on TV as the fire destroyed his house.
The Red Cross opened two shelters in the area — one at Yavapai College in Prescott and the other in a high school gym.