A 3-year-old boy died while trapped in a sweltering car amid a record-breaking heatwave in France and across Europe, according to authorities.

The tot climbed into the vehicle on Wednesday after his father told him to take a nap, but when he got inside, the car’s child-lock system activated — trapping him as temperatures rose above 85 degrees Fahrenheit in Saint-Gratien, Paris.

“He apparently shut himself in and became trapped in the vehicle before being found unconscious by his parents,” said public prosecutor Guirec Le Bras, citing preliminary findings from the investigation.

The boy was inside the car for 45 minutes before his parents found him unconscious. First responders failed to resuscitate him and he was later pronounced dead. 

Following the recovery of the tot’s body, his mother was hospitalized for shock.

Wednesday was France’s hottest day since officials began keeping records in 1947, with 72 départements — the primary territorial units in France — on high alert and 17 on moderate alert.

Average June temperatures in Paris range from around 57 degrees to 73 degrees Fahrenheit, according to the French government’s meteorological agency.

Experts warned that this week’s heatwave could surpass the lethality of France’s hot spell in 2003, which claimed 15,000 lives nationwide.

First deputy mayor of Paris Emmanuel Grégoire is calling on people to “be careful for their own sake,” adding that his country may have to become a “France of fans and a France of air conditioners,” Euronews reported.

Two other children — also found in their family car — died in Carpentras, in the southeastern part of the country.

Their causes of death are “yet to be determined,” Hélène Mourges, Carpentras’ town prosecutor, told the press. It is believed that the pair escaped their mother’s supervision and became trapped inside. 

Temperatures in Carpentras reached above 100 degrees Fahrenheit on Monday. 

Three elderly people between the ages of 80 and 95 have also died as a result of health issues caused by extreme temperatures. 

At least 48 others drowned in swimming accidents, authorities said. 

Experts said the “Euro heat dome” is caused by an “Omega block,” a high amount of pressure in the upper atmosphere, according to Weather.com. When the heat has nowhere to go, the dome inhibits any storms that would extricate the heat.