In its latest heatwave bulletin published on Saturday, the Italian health ministry says that by Monday, some 25 of the country's 27 major cities will be on red alert.
It says it expects only two - Reggio Calabria in the southern tip of Italy's "boot" and Messina, facing it across on the island of Sicily - to be on the second-highest "amber" alert.
The ministry urges residents in the affected areas to avoid exposure to heat and direct sunlight during the hottest hours between 11:00 and 18:00, stay indoors and drink plenty of fluids.
The extreme heat is being caused by a subtropical anticyclone from North Africa that is now strengthening over the Mediterranean.
Meanwhile, firefighters in Greece, France, Portugal and Spain are still tackling blazes spanning thousands of hectares.
In France, some 2,500 people were evacuated in the south-eastern Var region on Friday evening after a blaze - which had been contained for several days - reignited, local officials said.
But a massive fire in the south-western Gironde region is now under control, and some 200,000 local evacuated residents have been able to return to their homes.
In Greece, hundreds of people - mostly tourists - have been evacuated by sea from a coastal town of Viotia hemmed in by one of the many wildfires raging across the country.
And in Spain, more than 200,000 hectares of land has burnt in 2026 - roughly five times above the average by this point in the year - while the burnt land in Portugal is also higher than usual, EU data shows.
Climate change is driving up temperatures around the world, and Europe is the fastest warming continent, heating up twice as fast as the global average, according to the Copernicus Climate Change Service.
This is causing increased summer heatwaves, greater pressure on Europe's water supply, and more intense wildfires.
