Forty-nine of France's 96 regions are under a red heat alert, as the country braces for sweltering temperatures due to an intensifying heatwave.

Highs of more than 40C (104F) are expected across parts of western France on Monday, with the mercury expected to hit 43C in Bordeaux, according to weather forecaster Météo-France.

Some 845 schools have been shut for the day, while 1,800 students are being allowed to finish classes early, according to the ministry of education.

Dozens of other regions are under an orange alert, with an estimated 63 million people in total affected across the country.

The severe weather conditions follow a weekend in which the mercury hit 40C, prompting an alcohol ban at the annual Fête de la Musique, a national festival that sees large crowds celebrate on the streets of most cities.

In the south-west Gironde region, local authorities on Sunday said three people – aged between 80 and 95 years – had died, partly due to the intense heat.

Health Minister Stéphanie Rist told French public broadcaster TV1 Info on Monday that many "fellow citizens will suffer" during the hot weather, and called on people to keep a "close eye" on relatives and neighbours.

While the hottest temperatures are expected on the western coast, highs are expected to hang around 36C to 40C across much of the rest of the country, Météo-France said.

The forecaster warned that the heatwave will be "widespread, long-lasting and intense" – with temperatures not expected to drop until the end of the week.

The country's national railway operator SNCF urged "vulnerable" people to avoid or postpone train travel this week, while in Paris, several train lines reduced their services on Monday due to the heat.

Belgium's train operator also announced some peak hour trains would be cancelled for Monday and Tuesday.

Record high temperatures are also expected across Europe, with Madrid forecast to hit 39C while in Italy, it's predicted to hit 37C in Rome.