The Italian island of Sicily may have registered the hottest temperature ever recorded in Europe - 48.8C (119.8F).
Regional authorities reported the reading, which needs to be verified by the World Meteorological Organization (WMO), near Syracuse on Wednesday.
According to the WMO, the current official record in Europe is 48C, registered in Athens, Greece, in 1977.
The latest heatwave in Italy is being caused by an anticyclone - nicknamed Lucifer - moving up from Africa.
Anticyclones are areas of high atmospheric pressure where the air is sinking.
Lucifer is forecast to head north across mainland Italy, further raising temperatures in cities including the capital, Rome.
Italy's health ministry has issued "red" alerts for extreme heat in several regions and the number of cities that face the highest health risk is expected to rise from eight to 15 by Friday.
The Mediterranean heatwave, which has seen some countries record their highest temperatures in decades, has led to the spread of wildfires across southern Italy, with Sicily, Calabria and Puglia the worst-hit regions.
Italian firefighters on Wednesday said they had been involved in more than 300 operations in Sicily and Calabria over a 12-hour period, battling through the night to control blazes burning thousands of acres of land.
Three fire-related deaths - two in Calabria and one in Sicily - have been reported by Italian media.
Separately, wildfires are continuing across Greece, fuelled by strong winds and parched vegetation. Foreign teams are helping to tackle blazes in what Prime Minister Kyriakos Mitsotakis has described as a "nightmarish summer".
Climate change increases the risk of the hot, dry weather that is likely to fuel wildfires.
The world has already warmed by about 1.2C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.
On Monday the UN released a major report saying human activity was making extreme weather events more common.