PARIS — France gritted its teeth Monday for a week of record-busting temperatures, sweltering under a grueling heat wave that combines daytime highs above 40 degrees Celsius (104 Fahrenheit) and sleep-robbing sweaty nights.

The national weather service, Meteo France, said that most of the country — the largest in the European Union and second most populated — is entering what is described as a “plateau” of unrelenting heat-wave conditions that isn’t forecast to start easing before Friday at the earliest.

In a country without widespread air conditioning, people, businesses and services tried to adapt as best they could. Hundreds of schools were closed on Monday and many hundreds more were canceling some classes, the education minister said.

Broadcasts on the Paris transport network urged commuters to hydrate. Medical specialists took to the airwaves to warn of the potentially deadly cocktail of drinking alcohol in extreme heat. Authorities cracked down on alcohol consumption in public. Multiple drownings were reported as people sought relief in rivers, despite warnings about currents and other dangers.

Human-caused climate change is tied to increasing extreme weather, and U.N. climate agency projections say the next five years should shatter more heat records.

A growing swath of France, spreading on Monday to more than half of its regions, was under a “red alert” for heat, with larger areas forecast to suffer highs busting past 40 C and nights not dropping below 20 C.

In the United Kingdom, the weather office also issued an “extreme heat” warning for much of southern England and parts of Wales from Monday until Thursday. It said temperatures could reach 38 C (100 F). The current record for a June day is 35.6 C (96 F), reached in 1976.

Over the last four years, more than 200,000 people across Europe died from heat-related causes, and most of the fatalities were preventable, the World Health Organization’s Europe office said this month. More above-average temperatures are expected this summer, which can cause heat exhaustion and life-threatening heat stroke.