PARIS (AFP)

France issued a red heatwave alert across more than a third of the country for Sunday as a ferocious heatwave dug in.

The prolonged heatwave, which began earlier this week, has disrupted the country, forcing the cancellation of dozens of trains and the suspension of classes.

Authorities are also concerned about how the annual Fete de la Musique celebrations will unfold across the country on Sunday when musicians take over the streets with free performances.

"Very high temperatures are settling in for the long term across the country," Meteo-France said as it announced the highest heatwave warning for 35 of France's departments, or administrative regions, for Sunday.

Paris is one of the regions on the red-alert list.

According to AFP's calculations, around 26 million people are to be affected by the alert. Another 45 departments will be under orange alert.

To help Parisians and tourists cope with the heat, authorities are keeping parks and gardens in the French capital open through the night.