The reading was registered on Sunday at the Furnace Creek Visitor Center in the Death Valley national park by an automated observation system.
A temperature of 55.5 degrees Celsius recorded in California's Death Valley by the US National Weather Service is the hottest ever measured with modern instruments.
The reading was registered at 22:41 GMT on Sunday at the Furnace Creek Visitor Center in the Death Valley national park by an automated observation system, an electronic thermometer encased inside a box in the shade.
In 1913, a weather station half an hour's walk away recorded what officially remains the world record of 56.7 degrees Celsius.
But its validity has been disputed for a number of reasons: regional weather stations at the time didn't report an exceptional heatwave, and there were questions around the researcher's competence.
The next highest temperature was set in July 1931 in Kebili, Tunisia, at 55.0 degrees Celsius, but again, the accuracy of older instruments has been questioned.
In 2016 and 2017, weather stations in Mitribah, Kuwait and Turbat, Pakistan recorded temperatures of 54 degrees Celsius.
After evaluation by the World Meteorological Organisation both were downgraded by a few fractions of a degree.
The Geneva-based World Meteorological Organization said Monday it would start verifying the new US reading.
"This observed high temperature is considered preliminary and not yet official," said the US National Weather Service.
🥵Yep it was HOT out there today...— NWS Las Vegas (@NWSVegas) August 17, 2020
So hot in fact, that the PRELIMINARY high temperature @DeathValleyNPS was 130°F. If verified, this will be the hottest temperature officially verified since July of 1913. For more info...https://t.co/qFXcIVoPig#DeathValley #Climate #CAwx pic.twitter.com/lAl8NQDCyp
'On the fence'
Dan Berc, an official at the Las Vegas NWS office responsible for the site, told AFP that the sensor would be brought in for evaluation.
The investigation would take "at least a couple of months," he said, adding: "Growing up as a kid, I thought 130 degrees Fahrenheit [54.4 degrees Celsius] was a really cool record."
Validation isn't a formality, and long-held records have been thrown out after modern evaluation.
For decades, the heat record was officially the 58 degrees Celsius recorded in 1922 in El Azizia, now modern Libya.
But a WMO panel that investigated it in detail between 2010 and 2012 stripped it of the title after finding multiple troubling aspects, including a potential problem with the thermometers and an inexperienced observer.
Weather historian Chris Burt, who conducted an analysis in 2016 that disputed the 1913 record, said the meteorological community was "on the fence" about whether the new record was real.
"The suspicion about yesterday is that normally... all the stations are also reporting record high temperatures at the same time, and yesterday that wasn't the case," he told AFP.
Las Vegas, for example, only recorded 45 degrees Celsius.
On the other hand, he said, a tropical storm off the coast of the Baja California Peninsula had left a deep plume of moisture over much of California, which has resulted in large thunderstorms and localised heat surges.
"There was also a lot of convection in the mountains just west of Death Valley so there could have been some kind of effect downslope into Death Valley that really pushed up the temperatures," he added.
The southwestern US is currently enduring an intense heatwave. Scientists say such waves are becoming more frequent and dangerous because of human-driven climate change.
Worldwide, the five hottest years in history have occurred in the last five years.
Under the 2015 Paris Agreement, nations committed to limit temperature rises to "well below" -15.7 degrees Celsius above pre-industrial levels, mainly through sweeping emissions cuts.
These goals are seen as crucial to avoid triggering a series of tipping points that would cause irreversible global heating by the end of the century, making vast swaths of the planet inhospitable for life.
Michael Mann, a climate science professor at Pennsylvania State University, said: "As the planet continues to warm, it is inevitable that we will continue to see records fall."
If the new reading is confirmed, then "that record too shall fall soon enough," he added.