The hottest air temperature recorded anywhere on Earth in at least at century, and possibly ever, was reached in Death Valley in California's Mojave Desert on Sunday afternoon where it soared to 54.4°C.
An observation system run by the US National Weather Service at Furnace Creek reported the record at 3.41pm local time.
It was a dry heat, with humidity down to 7 per cent.
But it felt "insanely hot", said meteorologist Daniel Berc, who is based in the bureau's Las Vegas office.
Mr Berc forecast that the heatwave would continue all week.
"It's literally like being in an oven," he said. "Today is another day we could take another run at 130°F [54.4°C]."
A temperature of 56.7°C was recorded in Death Valley in July 1913.
But some meteorologists dispute that, with recent research pointing to the likelihood that it was the result of observer error.
"That's an official record until it's debunked through the scientific process and accepted by the World Meteorological Organisation," Mr Berc said.
Climate scientists are warning of the dangers with a warming planet.
Last month was the world's third-hottest July on record. Three of the hottest ever all occurred in the past five years.
Sunday's temperature will undergo a formal review, Mr Berc said.
Technicians will check to ensure the thermometer in Furnace Creek is working properly.
The weather bureau will convene a "climate extremes committee" to ensure there is no reason to doubt Sunday's data.