The lightning-sparked fire, which had ballooned to about 13 square miles by Monday morning, also destroyed dozens of homes and sent hundreds fleeing from Yarnell, a town of 700 residents about 85 miles northwest of Phoenix.
Residents huddled in area shelters and restaurants, watching their homes burn on TV as flames lit up the night sky in the forest above the town.
The fire killed 18 members of a 20-member "hotshot" crew based in nearby Prescott, Arizona State Forestry Division spokesman Mike Reichling said.
Officials originally said all 19 people killed were members of the crew. But Reichling told The Associated Press on Monday that one of the 19 was not a member. The man was presumed to be a firefighter but has not been identified, Reichling.
It is unknown how the crew became trapped with no escape route as members attempted to save Yarnell from the fast-growing blaze, which covered at least 3 square miles Sunday amid triple-digit temperatures. The team had spent recent weeks fighting fires in New Mexico and Prescott before being called to Yarnell, entering the smoky wilderness over the weekend with backpacks, chain saws and other heavy gear used to remove brush and trees.
The disaster all but wiped out the Prescott hotshot crew, leaving the city's fire department reeling.
"We grieve for the family. We grieve for the department. We grieve for the city," Prescott Fire Chief Dan Fraijo said at a news conference Sunday evening. "We're devastated. We just lost 19 of the finest people you'll ever meet."
A makeshift memorial including flower bouquets and American flags formed at the Prescott fire station where the crew was based. Longtime Prescott resident Keith Gustafson showed up at the site and placed 19 water bottles in the shape of a heart, and planned to go to the scene to hand out more water.
"When I heard about this, it just hit me hard," he said. "It hit me like a ton of bricks."
Hotshot crews go through specialized training and often are deployed soon after a fire breaks out. Sometimes they hike for miles into the wilderness with chain saws and backpacks filled with heavy gear to build lines of protection between people and fires. They remove brush, trees and anything that might burn in the direction of homes and cities. This crew had worked other wildfires in recent weeks in New Mexico and Arizona.
As a last-ditch effort at survival, members are trained to dig into the ground and cover themselves with the tent-like shelter made of fire-resistant material, Fraijo said. The hope in that desperate situation is that the fire will burn over them and they will survive.
"It's an extreme measure that's taken under the absolute worst conditions," Fraijo said.
Nineteen fire shelters were deployed, and some of the firefighters were found inside them, while others were outside the shelters, Reichling told the Arizona Republic.
More than 200 firefighters and support personnel were assigned to the wildfire as of Monday morning. They included a top-level management team and 18 hotshot crews from around the country. Such crews typically have about 20 members each.
The number of hotshot crews assigned to the fire is expected to at least double, Reichling said.
Spokesmen for fire managers did not immediately respond to requests for comment early Monday.
Arizona is in the midst of a historic drought that has left large parts of the state dried out. The U.S. government granted a disaster designation to the county where the fire occurred because of the drought.
The National Weather Service said there's a 30 percent of thunderstorms and showers Monday in the Yarnell area. Rain could help slow the fire, but the forecast also says the storms could produce gusty winds.
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 most firefighters — 343 — were killed in the 9/11 terrorist attacks 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, and the city also has 75 suppression team members.
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.
"This is as dark a day as I can remember," Gov. Jan Brewer said in a statement. "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."
Brewer said she would travel to the area Monday.
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 model 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 gathered at the Arrowhead Bar and Grill in nearby Congress along with locals and watched on TV as he saw the fire destroy his house.
Two hundred firefighters were working on the fire Sunday, and several hundred more were expected to arrive Monday.
The fire has forced the closure of parts of state Route 89. Fire crews had no containment late Sunday.
The Red Cross has opened two shelters in the area — at Yavapai College in Prescott and at the Wickenburg High School gym.