The firefighters were battling the Yarnell Hill blaze 135 kilometres north-west of Phoenix. The fire is estimated to have destroyed half the town of Yarnell, the Arizona Republic said.
"It is a dark day," said Mike Reichling, Arizona State Forestry Division spokesman.
He identified the victims as members of the Granite Mountain Hotshots, an elite team typically sent in first to help cut offfires. The team had deployed emergency heat shelters but did not survive the intensity of the flames when the fire quickly turned, according to the report.
The fire occurred on a weekend of record temperatures across the western US, with Death Valley in eastern California recording a temperature of 54 degrees, according to the Los Angeles Times.//DPA