Britain has shattered its record for the highest temperature ever registered, with a provisional reading of 40.2 degrees Celsius (104.4 degrees Fahrenheit) at Heathrow Airport - breaking the record set just an hour earlier, the weather office said Tuesday.

Before Tuesday, the highest temperature recorded in Britain was 38.7 C (101.7 F), a record set in 2019.

The high Tuesday came as the country sweltered in a heat wave that also scorched mainland Europe for the past week. Travel, health care and schools were disrupted in a country not prepared for such extremes.

Parts of England are under a "red" alert, a warning for extreme heat that poses a risk of serious illness and even death among healthy people.

The U.K.’s Met Office weather agency said provisional figures showed the temperature remained above 25 degrees Celsius overnight in parts of the country for the first time.

Met Office forecaster Rachel Ayers said Tuesday’s highs would be "unprecedented.”

"The temperature will be very hot throughout the day, before rising as high as 40 Celsius, maybe even 41 Celsius in isolated spots across England during the afternoon,” she said.

A huge chunk of England, from London in the south to Manchester and Leeds in the north, is under the country’s first warning of "extreme” heat, meaning there is a danger of death even for healthy people.

Hot, dry weather has gripped southern Europe since last week, triggering wildfires in Spain, Portugal and France, before moving north.

The temperature Monday reached 38.1 degrees Celsius in Santon Downham in eastern England, just shy of the highest-ever temperature recorded in Britain – 38.7 degrees.

Average July temperatures in the U.K. range from a daily high of 21 degrees to a night-time low of 12 degrees, and few homes or small businesses have air conditioning.

Many people coped with the heat wave by staying put. Road traffic was down from its usual levels on Monday. Trains ran at low speed out of concern for buckled rails or did not run at all. London’s Kings Cross Station, one of the country’s busiest rail hubs, was empty on Tuesday, with no trains on the busy east coast line connecting the capital to the north and Scotland. London’s Luton Airport had to close its runway because of heat damage.

Transport Secretary Grant Shapps said Britain’s transport infrastructure, some of it dating from Victorian times, "just wasn’t built to withstand this type of temperature – and it will be many years before we can replace infrastructure with the kind of infrastructure that could.”

At least five people were reported to have drowned across the U.K. in rivers, lakes and reservoirs while trying to cool off.

Climate experts warn that global warming has increased the frequency of extreme weather events, with studies showing that the likelihood of temperatures in the U.K. reaching 40 degrees Celsius is now 10 times higher than in the preindustrial era. Drought and heat waves tied to climate change have also made wildfires harder to fight.

The dangers of extreme heat were on display in southern Europe. Almost 600 heat-related deaths have been reported in Spain and Portugal, where temperatures reached 47 degrees Celsius last week.

In the Gironde region of southwestern France, ferocious wildfires continued to spread through tinder-dry pines forests, frustrating firefighting efforts by more than 2,000 firefighters and water-bombing planes.

More than 37,000 people have been evacuated from homes and summer vacation spots since the fires broke out on July 12 and burned through 190 square kilometers (more than 70 square miles) of forests and vegetation, Gironde authorities said.

A smaller third fire broke out late Monday in the Medoc wine region north of Bordeaux, further taxing firefighting resources. Five camping sites went up in flames in the Atlantic coast beach zone where blazes raged around the Arcachon maritime basin famous for its oysters and resorts.

But weather forecasts offered some consolation, with heat wave temperatures expected to ease along the Atlantic seaboard Tuesday and the possibility of rains rolling in late in the day.