At least 19 US firefighters are reported to have been killed while tackling a wildfire in central Arizona.
They died while battling the blaze threatening the town of Yarnell, about 80 miles north-west of Phoenix.
The fire was started by lightning on Friday and spread rapidly amid high heat, low humidity and strong winds.
This came as Arizona and other parts of the western US – including California – recorded near-record temperatures over the weekend.
Dozens of people across western US states have been treated for exhaustion and dehydration, as the heat wave continues.
US Airways was forced to cancel 18 flights at the weekend as temperatures exceeded safe levels in the Southwest. Under safety regulations, aircraft can take off at up to 118 degrees, but the temperature reached 119 in Phoenix, Arizona on Saturday.
Temperatures in some areas were expected to reach 54C (130F), close to the world’s all-time high recorded 100 years ago in California’s Death Valley, the BBC reported.
The Foreign & Commonwealth Office said: “Forest and brush fires (wild fires) are a danger in many dry areas. High winds can cause fires to spread very rapidly. Areas of high risk are canyons, hills and forests. Monitor local media reports and follow the advice of local law enforcement officials.”