French firefighters have been mobilised to tackle early summer fires as 84 of the country's 101 administrative areas were put on a heatwave alert from tomorrow until midweek.
Wildfires broke out in the Corbières area of Aude in the southwest, where temperatures topped 40C, forcing the evacuation of a campsite and abbey as a precaution.
The south of the country saw highs of more than 40C, with temperatures between 35 and 38C across the region, national weather service Meteo-France said.
It reported a temperature of 40.9C in the small town of Grospierres in southeastern France, 40.1C in the village of Vinsobres in the southeast and 39.9C in the town of Cadenet, also in the southeast.
The crushing temperatures which began in the south of the country on Friday will have spread to nearly all of France tomorrow, with highs of 37 to 40C forecast along the Mediterranean.
The number of departments under orange alert - the second-highest level - will rise to 84 tomorrow, with temperatures expected to peak Tuesday and Wednesday, bringing highs of up to 41C.
An interministerial crisis meeting on the heatwave was convened to review all the guidelines, particularly concerning health, Interior Minister Bruno Retailleau told BFMTV.
Some cities have already closed schools for the beginning of the week as a protective measure.
The heatwave spans southern Europe, from Italy to Portugal, where Lisbon and several regions are on red alert, with authorities urging people to seek shelter and protect the most vulnerable.
Ambulances stood on standby near tourist hotspots and regions issued fire warnings as experts warned that such heatwaves, intensified by climate change, would become more frequent.
In Spain, temperatures reached 46C yesterday in El Granado.
The heatwave is driven by a heat dome - a strong anticyclone that traps warm air and prevents cooler systems from entering.
In Italy, 21 cities are on high alert for extreme heat, including Milan, Naples, Venice, Florence and Rome.
"We were supposed to be visiting the Colosseum, but my mum nearly fainted," said British tourist Anna Becker, who had travelled to Rome from a "muggy, miserable" Verona.
Hospital emergency departments across Italy have reported an uptick in heatstroke cases, according to Vice President of the Italian Society of Emergency Medicine Mario Guarino.
"We've seen around a 10% increase, mainly in cities that not only have very high temperatures but also a higher humidity rate.
"It is mainly elderly people, cancer patients or homeless people, presenting with dehydration, heat stroke, fatigue," he said.
'Climate shelters'
Hospitals like the Ospedale dei Colli in Naples have set up dedicated heatstroke pathways to speed access to vital treatments like cold water immersion, Mr Guarino said.
In Venice, authorities offered free guided tours for people over 75s in air-conditioned museums and public buildings.
Bologna has set up seven "climate shelters" with air conditioning and drinking water, Florence has called on doctors to flag up the lonely and vulnerable, Ancona is delivering dehumidifiers to the needy, and Rome has offered free access to city swimming pools for those over 70.
Scientists say climate change is stoking hotter and more intense heatwaves, particularly in cities where the so-called "urban heat island" effect amplifies temperatures among tightly packed buildings.
"The heatwaves in the Mediterranean region have become more frequent and more intense in recent years, with peaks of 37C or even more in cities, where the urban heat island effect raises the temperatures even further," said Emanuela Piervitali, a researcher at the Italian Institute for Environmental Protection and Research (ISPRA).
"A further increase in temperature and heat extremes is expected in the future, so we will have to get used to temperatures with peaks even higher than those we are experiencing now," she said.
In Portugal, several areas in the southern half of the country, including the capital Lisbon, are under a red warning for heat until tomorrow night due to "persistently extremely high maximum temperature values", according to the Portuguese Institute for Sea and Atmosphere (IPMA).
Two-thirds of Portugal was on high alert for extreme heat and forest fires, as was the Italian island of Sicily, where firefighters tackled 15 blazes yesterday.
In France, experts warned that the heat was also severely impacting biodiversity.
"With this stifling heat, the temperature can exceed 40C in some nests," said President of the League for the Protection of Birds (LPO) Allain Bougrain-Dubourg.
"We are taking in birds in difficulty everywhere; our seven care centres are saturated," he said.
It is also attracting invasive species, which are thriving in the more tropical climes.
Italy's ISPRA launched a campaign this week urging fishermen and tourists alike to report sightings of four "potentially dangerous" venomous species.
The lionfish, silver-cheeked toadfish, dusky spinefoot and marbled spinefoot are beginning to appear in waters off southern Italy as the Mediterranean warms, it said.
