A so-called "heat dome" of warm air from northern Africa trapped under a high-pressure system over western Europe is behind the high temperatures not usually seen until high summer.

Temperatures in Spain were expected to peak later this week at 38C, while parts of Italy imposed restrictions on working outdoors.

In the UK, the Met Office weather agency said it was the hottest May day on record, with temperatures hitting 34.8C at Kew Gardens, southwest London -- a full two degrees above the previous high.

"This heat would be exceptional in the UK even in mid-summer, let alone May," it said on X.

"The weather here, it's like a mini version of hell. It's boiling. It's like really hot," said 10-year-old Liza Nizari on a visit to London, where temperatures normally average about 17C or 18C at this time of year.

Lindy Brand-Daloze, a 66-year-old Australian administrator who has been living in in London for 12 years, said: "It's warm, but it's climate change, isn't it? So, you know, (we have) probably got to get used to this."

Scientists say human-induced climate change is making extreme weather events like heatwaves, droughts and floods more intense, resulting in temperature records being broken more frequently.

Met Office meteorologist Greg Dewhurst told AFP the increase in extreme temperatures was "a good indication of climate change in action" and more likely to become "the new norm".

Climate advisers last week warned the UK government that the country was "built for a climate that no longer exists" and urged it to adapt infrastructure like schools and hospitals for a warming planet.

In 2022, temperatures in the UK soared above 40C for the first time since records began.

- Heatwave alert -

Across the Channel, weather agency Meteo-France said "dozens" of temperature records were broken in several French cities, as it placed eight western regions under a heatwave alert.

The exceptionally high temperatures were expected to last until the weekend.

On Monday, the western town of Bergerac recorded a high of 34.7C, with the cities of Nantes and Angers not far behind.

On Tuesday, heat of between 32C and 35C was expected across much of the western region of Brittany, "with peaks of 36C or even 37C expected in the south of the country", Meteo-France said.

French Prime Minister Sebastien Lecornu was to hold a meeting Thursday with key ministers to go over government preparations for the heatwave.

The capital, Paris, on Saturday notched up its first temperature above 30C of the year, hitting 31.9C.

On Sunday, a man died during a 10-kilometre running race in Paris, civil defence services said, while 10 more had to be taken to hospital in critical condition after a race in the capital's suburb of Maisons-Alfort, the authorities said.

A 28-year-old woman also died of heatstroke at an indoor athletics meeting in the eastern Rhone region.

- Outdoor work restricted -

In Spain, the State Meteorological Agency (Aemet) warned the "extraordinarily high temperatures for this time of year" will continue across the country all week, except in the Canary Islands, in the Atlantic Ocean, off the northwest coast of Africa.

"Widespread tropical nights" are also forecast in southwestern Spain from Wednesday, with temperatures peaking from Wednesday to Friday at between 36C and 38C, it wrote on X.

Farther east, Italy's Lazio region, which includes Rome, on Monday approved rules limiting work in conditions "with prolonged exposure in the sun" between 12:30 pm and 4:00 pm.

The measures apply, for example, to farms, construction sites and in the logistics sector and apply until September 15.

Similar rules had been put in place last year but only from May 30.

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