PHOENIX (REUTERS) - An Arizona wildfire that killed 19 firefighters is 80 per cent contained, though hundreds of evacuated residents are still unable to return home, fire officials said on Thursday.

More than 600 firefighters had dug trenches to control the 3,400ha blaze and it is expected to be contained by noon on July 12, the Arizona State Forestry Division said in an online status report.

Authorities are allowing some residents evacuated from their homes to return, it said.

The 19 men died on Sunday as they battled the fast-moving fire as it menaced Yarnell, a small town near Prescott in central Arizona.

The fire swept over them in rugged mountainous terrain, forcing the men to scramble into individual emergency foil shelters, a last resort for wildland firefighters.

The Maricopa County Medical Examiner's Office determined that all 19 died of accidental fire-related injuries.

Fire-related injuries can involve burns or inhalation problems or both, said Maricopa County communications director Cari Gerchick.

"I can't tell you who had what, who had one or the other or both. All of those details will be available when the autopsy reports are released in a few months," Ms Gerchick said.

The last known photo of the men, all members of the Prescott Fire Department's Granite Mountain Hotshots, shows one man standing and two resting on boulders on a hillside overlooking the smoking inferno.

Mr Andrew Ashcraft, 29, who died in the fire, texted the picture to his wife shortly before the fire overtook the crew, according to a caption on the crew's Facebook page.

About US$800,000 (S$1 million) had been raised for the families of the victims as of Thursday, according to YarnellFallenFirefighters.com.