Seventeen departments of France – in the north-west, as well as Paris – are under an orange alert, indicating people should be “very vigilant” about the weather.
Temperatures are expected to reach 33C in Paris on Thursday, and top out at 34C on both Saturday and Sunday.
Police have announced measures to ease traffic in the capital until Saturday, including only allowing lower-emission cars on roads and lowering speed limits. A single fare for the entire public transport network will be offered at the same time.
At the French Open in Paris, Sinner appeared to be cruising to a victory before suddenly taking a turn for the worse.
The Italian complained of dizziness and feeling lethargic before hitting a wall.
“It was a tough spot to be in,” he commented afterwards, but added: “Really it was nothing against the heat, nothing against the weather. It was just me today, but it happens.”
Meanwhile, Italy’s red alert in Rome – as well as in Florence, Bologna, Brescia and Turin – is the first of the year, warning of “possible negative effects on the health of healthy, active people”.
Temperatures will climb to 35C in Madrid over the weekend. Though the current spell does not officially qualify as a heatwave in Spain, the nation’s meteorological office has said the heat is that usually seen in July and August.