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.

"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."

The Met Office weather agency said Monday was the hottest May day on record, with the mercury rising to 33.5C at Heathrow, west of the capital, at 1:00 pm (1200 GMT) -- 1.3C more than the previous benchmark recorded in 1922 and 1944.

"Records are usually only broken by tenths of a degree -- making this heatwave unprecedented for the time of year," the agency said in a social media post.

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 put eight areas in the west of France on heatwave alert -- signifying three days and nights of intense heat that are likely to pose a health risk to the population.

In the northwestern city of Rennes, 74-year-old Daniele Dupont tried to stick to the shade as she walked her dog in 27C on Monday morning.

"I'm going to close the shutters. I won't be going out this afternoon," she said in the capital of the Brittany region.

On Sunday, "record high maximum temperatures for the month of May" were felt in at least 10 locations, including the northwestern seaside towns of Lorient and Noirmoutier.

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

Temperatures of up to 35C are expected in Brittany and between 36C and 37C in the south.

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

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.

burs-phz/rmb