The National Weather Service (NWS) said the temperature was recorded near Furnace Creek, close to the Nevada border, at around 3.41pm on Sunday.
“This observed high temperature is considered preliminary and not yet official,” a statement from NWS Las Vegas said.
The reading will be further investigated by the National Center for Environmental Information and the World Meteorological Organisation (WMO).
The current record for the hottest temperature ever recorded on Earth was also logged in Death Valley, according to the WMO.
A temperature of 56.7C (134F) was recorded at Greenland Ranch on 10 July 1913. That recorded was installed after the WMO struck off the previous record of 58C recorded in Libya in September 1922.
Experts said the Libya reading was incorrect due to human error, the type of thermometer used and inconsistencies with other temperatures in the region.
But Christopher Burt, who prompted the investigation into the Libya reading, and who works for a private US meteorological service, has cast doubt on the 1913 Death Valley record.
He claimed in a 2016 article that the 1913 record was “essentially not possible from a meteorological perspective”.
One expert has said that he is confident the temperature recorded in Death Valley over the weekend will stand.
Professor Randy Cerveny, of Arizona State University and who leads a WMO group that maintains an archive of climate extremes, told the Washington Post: “Everything I’ve seen so far indicates that is a legitimate observation.”
He has recommended that the WMO accept the 54.4C recorded over the weekend.
This means that, if Sunday’s temperature is confirmed, and the 1913 reading is later struck off, then the 129.9F (54.4C) logged near Furnace Creek on Sunday will become the hottest ever temperature recorded on Earth.
The temperature came as a number of wildfires raged through California as record-breaking heatwave gripped the state, causing power outages.
Lightning strikes sparked new fires in northern California on Sunday. The rare thunderstorm also exacerbated a huge forest fire that has already forced hundreds from their homes north of Los Angeles.
Some 4,500 buildings remain threatened by the blaze, which was burning towards thick, dry brush in the Angeles National Forest.
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