Britain’s first-ever extreme heat warning is in effect for large parts of England as authorities prepare for record high temperatures that are already disrupting travel, health care and schools.

The “red” alert will last throughout Monday and Tuesday when temperatures may reach 40 degrees Celsius (104 Fahrenheit) for the first time, posing a risk of serious illness and even death among healthy people, according to the U.K. Met Office, the country’s weather service. The highest temperature ever recorded in Britain is 38.7C (101.7F), a record set in 2019.

“We need to recognize that there are some people who will not cope well in the heat and what we want is for everybody to look out for them,’’ Cabinet Office Minister Kit Malthouse said.

Train operators are asking customers not to travel unless absolutely necessary because the heat is likely to warp rails and disrupt power supplies, leading to severe delays. Some medical appointments have been canceled to relieve strain on the health service. While some schools have closed, others are setting up wading pools and water sprays to help children cool off.

The Met Office’s chief meteorologist, Paul Davies, warned that Monday night will be “very oppressive” and it will be difficult to sleep in the heat.

“And tomorrow is the day where we are really concerned about a good chance now of hitting 40 or 41C, and with that all the health conditions that come with those higher temperatures,” Davies said.