A temperature of 54.4 degrees Celsius (130 degrees Fahrenheit) recorded in California's Death Valley could be the hottest ever measured with modern instruments.
The reading was registered at 3:41 pm 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 134°F (56.7°C).
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 131°F (55°C) - but again, the accuracy of older instruments has been questioned.
In 2016 and 2017, weather stations in Kuwait and Pakistan recorded temperatures of 129.2°F (54°C), but the evaluation by the World Meteorological Organization both were downgraded by a few fractions of a degree.
Verification process begins
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.
Dan Berc, an official at the Las Vegas NWS office responsible for the site says 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° Fahrenheit 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 136.4°F (58°C) 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 over potential irregularities.
The potential world record comes as the southwestern United States is currently enduring an intense heat wave. 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" two 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.