The alert covers large parts of England on Monday and Tuesday when temperatures may reach 40 Celsius (104 Fahrenheit) for the first time, posing a risk of serious illness and even death among healthy people, the U.K. Met office said Friday. The British record is 38.7C (101.7F), set in 2019.

Rail passengers and users of the London Underground are being advised not to travel on Monday and Tuesday unless it is absolutely necessary. With children and older people considered particularly vulnerable to high temperatures, schools and care homes have been urged to take steps to protect students and older residents.

“If customers do need to travel, they should check before they travel as we are expecting there to be some impact to Tube and rail services as a result of temporary speed restrictions we will need to introduce to keep everyone safe,” said Andy Lord, chief operating officer of Transport for London, which runs the capital’s transportation system.

The alert comes as scientists say climate change is increasing the likelihood of exceptional heat waves in Britain, a country unaccustomed to such temperatures.