Britain’s Met Office issued its first ever “red” warning for exceptional heat, saying record temperatures early next week will put even healthy people at risk of serious illness and death.

The warning covers Monday and Tuesday, when temperatures in England may reach 40 degrees Celsius (104 degrees Fahrenheit) for the first time, the agency said. The highest temperature ever recorded in the U.K. is 38.7C (101.7F), set in 2019.

“We hoped we wouldn’t get to this situation but for the first time ever we are forecasting greater than 40°C in the U.K.,” said Nikos Christidis, a Met Office scientist. “In a recent study we found that the likelihood of extremely hot days in the U.K. has been increasing and will continue to do so during the course of the century, with the most extreme temperatures expected to be observed in the southeast of England.”

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The U.K. Health Security Agency increased its own alert to the highest level, warning of a “national emergency.”

‘’At this level, illness and death may occur among the fit and healthy, and not just in high-risk groups,” UKHSA said.

The two agencies issued lower-level warnings earlier this week as large parts of the U.K. experienced higher than normal temperatures, although cooler weather prevailed Thursday and Friday. Temperatures are expected to build over the weekend before peaking Monday and Tuesday.

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The weather alert, which covers a big chunk of England from London north to Manchester, also warns of potential disruption to air and rail travel and potential “localized loss of power and other essential services, such as water or mobile phone services.”

“If people have vulnerable relatives or neighbors, now is the time to make sure they’re putting suitable measures in place to be able to cope with the heat because if the forecast is as we think it will be in the red warning area, then people’s lives are at risk,’’ Met Office spokesman Grahame Madge said. “This is a very serious situation.”