This story originally appeared in The Guardian and is republished here as part of the Climate Desk collaboration.

Two children, aged 4 and 2, have been found dead in their family’s car in south eastern France, the local prosecutor said, as a large swathe of western Europe suffers a ferocious heatwave forecast to shatter absolute temperature records.

“The causes of death are yet to be determined, but the heat is the leading line of inquiry,” said Hélène Mourges, the prosecutor in the town of Carpentras, where the temperature was expected to exceed 39°C (102.2°F) on Monday afternoon.

The deaths follow those of three elderly people, aged between 80 and 95, who died ⁠near Bordeaux over the weekend as a result of health problems caused by the extreme temperatures, an official said. Thirteen more drowned in swimming accidents.

French authorities on Monday placed half the country — 49 of the country’s 96 mainland departments — on a level 1 danger-to-life warning, urging 35 million people to exercise “absolute vigilance,” avoid strenuous exertion, and stay out of direct sun.

A further six departments will be added to the red list on Tuesday, with 35 others remaining on a level 2 orange alert. “Very high temperatures are setting in for the long term across the country,” said the national weather service, Météo-France.

It said temperatures throughout western and central France were likely to exceed 40°C from Monday afternoon — hitting 43°C in Bordeaux, 41°C in Limoges, 40°C in Toulouse and Tours and 39°C in Paris — and would continue rising until the end of the week.

Nighttime lows are also likely to be far higher than normal until at least Friday, Météo-France said, with the minimum temperatures of about 25°C recorded in several towns and cities overnight on Sunday already setting all-time records.

France’s so-called national heat index, an average of the day and nighttime highs measured at 30 weather stations around the country, is expected to hit its highest ever level on Monday or Tuesday, the forecaster said.

More than 1,300 schools were closed nationwide on Monday, while another 4,000 rescheduled classes to allow pupils to leave early. One in 10 regional train services around Paris were cancelled amid fears for rolling stock and tracks.

“Many people are going to suffer, because bodies suffer from an accumulation of high temperatures,” said Stéphanie Rist, France’s health minister, visiting a Paris hospital on Monday. She urged people to check on elderly and vulnerable neighbours.

“We’re heading for, at the very least, several days of very, very hot weather. We really don’t know when temperatures will start falling,” Rist later told French television.

France went ahead with its annual street music festival, the Fête de la Musique, on Sunday, although some local authorities called it off altogether, and others ran only evening events. Alcohol restrictions were imposed in many areas.

Spain declared its first official heatwave of the year from Sunday until Wednesday, with temperatures forecast to reach 44°C in some areas. A public screening in Madrid of the national football team’s World Cup match against Saudi Arabia was cancelled.

The state weather service, Aemet, warned on Sunday of “extremely high” day and night temperatures and issued a red alert for the northern Basque region, where the city of San Sebastián was forecast to hit 40°C, more than double the seasonal average.

“We are seeing temperatures between 5 and 10 degrees above normal for this time of year, and in some northern areas ​even more than 10 degrees above average,” said Rubén del Campo, a spokesperson for the meteorological agency.

In Germany, organisers suspended the final of the Berlin Open tennis tournament and cleared everyone out of the event location because of severe thunderstorms as temperatures in the German capital topped 30°C over the weekend.

Temperatures in Belgium — already past 30°C on Sunday — would be “the hottest ever recorded,” said David Dehenauw, the head of forecasting at the IRM weather institute. Some rush-hour trains were cancelled to limit the risk of breakdowns.

In the UK, the Met Office national weather service issued an “extreme heat” warning for much of southern England and parts of Wales until Thursday, predicting temperatures of up to 39°C. The current record for a June day is 35.6°C, set in 1976.

Italy on Monday issued heatwave red alerts for 12 cities, including Milan, ​Turin, Venice, Bologna, Florence, and Rome.

Scientists have said that as the Earth continues to warm, extreme heat events historically confined to high summer will become more frequent, more intense, and last longer, as well as happening earlier and later in the year.