Nineteen firefighters from an elite team in Arizona were killed while battling a fast-moving wildfire in the US state.

The fires have destroyed scores of homes and forced the evacuation of two small towns northwest of Phoenix, the state capital.

The tragedy is ranked as the greatest loss of life among firefighters from a single wildfire in the US in 80 years, since 29 men died battling the Griffith Park fire of 1933 in Los Angeles.

Art Morrison of the Arizona State Forestry Commission told CNN the firefighters, members of a specially trained "hot shot" team, lost their lives yesterday when they were overtaken by swiftly moving flames.

"It was a hand crew, a hot shot crew," he said.

"In normal circumstances, when you're digging fire lines, you make sure you have a good escape route, and you have a safety zone set up.

“Evidently, their safety zone wasn't big enough, and the fire just overtook them. By the time the other firefighters got in, they didn't survive," Mr Morrison said.

The crew was initially reported missing before word came from the US Wildland Fire Aviation service that the team had died in the blaze, which erupted on Friday near the small town of Yarnell about 128km northwest of Phoenix.

Prescott Fire Chief Dan Fraijo called the tragedy "one of the worst wildfire disasters that's ever taken place".

He said he did not know the circumstances that led to the 19 deaths.

He said one member of the 20-man crew happened to be in a separate location and survived. There was no immediate information on his condition.

The blaze, stoked by strong, dry winds and a heatwave that has baked the region in triple-digit temperatures, has charred about 2,000 acres of tinder-dry chaparral and grasslands, fire officials said.

Local television news footage showed an unbroken line of flames stretching along a ridgeline, sending gray brown smoke billowing into the evening sky.

Authorities ordered the evacuation of Yarnell and the adjoining town of Peeples Valley, alerting residents through reverse 911 emergency calls to homes and sending sheriff's deputies door to door.

The two towns, which lie southwest of Prescott, Arizona, are home to roughly 1,000 people.

Steve Skurja, spokesman for Yavapai County Sheriff's Office, said at least 200 structures have been destroyed by the fire, most of them in Yarnell, a community consisting largely of retirees.

The Daily Courier Prescott newspaper said the dead were members of the Prescott Fire Department's Granite Mountain Hotshots team.

"This is as dark a day as I can remember," Governor 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."