A three-year-old has died after finding himself trapped in a car in the Paris region in extreme heat, a prosecutor said on Thursday, the third such fatality this week.

The boy had slipped into the family car while his father thought he was napping, then found himself unable to get out with the child lock in the town of Saint-Gratien, the prosecutor said, after a police source and civil defence also reported the death.

France on Wednesday recorded the hottest day since measurements began in 1947, the average temperature reaching 30 degrees Celsius (86 degrees Fahrenheit).

Temperatures in the capital reached 40.3 degrees on the same day, topping 40 degrees for the fourth time in 150 years.

The boy died after his parents and firefighters failed to resuscitate him, public prosecutor Guirec Le Bras said.

The mother was having a nap with the couple’s second child, an 18-month-old, while the father was working in a shed in the garden, he said, citing initial findings.