Italy put 23 cities on red alert with temperatures set to reach up to 46C, one of the global hotspots as a wave of extreme heat, wildfires and flooding wreaks havoc from the United States to China.
The heatwave has hit southern Europe during the peak summer tourist season, breaking records including in Rome and bringing warnings about an increased risk of deaths.
The Lazio region, focused on Rome, said it had seen a 20 per cent increase in medical emergencies over the same time last year because of the heat.
Wildfires burned for a third day west of the Greek capital Athens and firefighters worked throughout the night to keep flames away from coastal refineries.
Fanned by erratic winds, the fires have gutted dozens of homes, prompted hundreds of people to flee and blanketed the area in thick smoke. Temperatures could climb to 43C on Thursday, forecasters said.
In China, which was hosting US climate envoy John Kerry for talks, tourists defied the heat to visit a giant thermometer showing surface temperatures of 80C.
In Beijing, which set a new record as temperatures remained above 35C for the 28th day in a row, Kerry expressed hope that cooperation to combat global warming could redefine troubled ties between the two superpowers.
A global pattern of heatwaves that scorched parts of Europe, Asia and the United States this week has thrown that challenge into sharp relief.
Temperatures remained high across much of Italy on Wednesday, with 45-46C expected on the Mediterranean island of Sardinia.
The health ministry said it would activate an information hotline and teams of mobile health workers visited the elderly in Rome.
"These people are afraid they won't make it, they are afraid they can't go out," said Claudio Consoli, a doctor and director of a health unit.
Carmaker Stellantis said it was monitoring the situation at its Pomigliano plant near Naples on Wednesday, after temporarily halting work on one production line the day before when temperatures peaked.
Workers at battery-maker Magneti Marelli threatened an eight-hour strike at their central Italian plant in Sulmona. A joint statement by the unions said "asphyxiating heat is putting at risk the lives of workers".
While the heatwave appears to be subsiding in Spain, residents in Greece were left surveying the wreckage of their homes after the wildfires.
"Everything burned, everything. I will throw it all," said Abbram Paroutsidis, 65.
Not everyone went willingly. Footage by Greek police showed officers imploring a reluctant group of nuns to evacuate a convent.
Scientists have long warned that climate change, caused by greenhouse gas emissions mainly from burning fossil fuels, will make heatwaves more frequent, severe and deadly.
In Germany, the heatwave sparked an unlikely discussion on whether workplaces should introduce siestas for workers.
El Corte Inglés, one of Spain's largest department store chains, said sales of air conditioning units had jumped, as had interest in cooling pads for pets.
"The current extreme heat is due mainly to a slow-moving anticyclone, a high-pressure system, that is dominating the upper atmosphere over southern Europe," explained Florian Pappenberger, Director of Forecasts at ECMWF.
"While the current heatwave is expected to last until around 26 July, another period of extreme temperatures may follow if the heat dome persists."
Elsewhere in the world, it is the increased rainfall that is doing damage.
Some 38 people have died as a result of heavy rains in South Korea, while the Yamuna river reached the compound walls of the Taj Mahal in Agra for the first time in 45 years.
Northern India has been hit with flash floods, landslides and accidents since the start of June, with rainful at 41 per cent above the average.
