According to local authorities, the elderly couple died in the seaside town of Le Lavandou and one other person in the town of Vidauban.

The couple's vehicle was swept away by floodwaters.

The woman's body remained trapped inside the wreckage, Toulon public prosecutor Samuel Finielz told AFP.

An investigation has been opened to determine the cause of death, he said, adding that "the situation was quite difficult on the ground".

Gil Bernardi, mayor of Le Lavandou, described "scenes of war", "roads torn up" and "bridges torn down."

"It was a really violent, vicious, incomprehensible phenomenon," Bernardi told BFM television.

"There is nothing left, no electricity, no drinking water, no sewage treatment plant," he added.

In Vidauban, a local official pulled a driver from her vehicle but the passenger could not be saved.

"A driver and her passenger drove onto a country road that was completely submerged" and the car fell into a ditch, the mayor, Claude Pianetti, said on Facebook.

Hailstorms and heavy rain also hit southwestern France a day earlier, flooding homes, damaging railway tracks and forcing the evacuation of hundreds of passengers aboard a high-speed TGV train in the middle of the night.

The TGV, on its way from Toulouse to Paris late Monday, was on a track that became dislodged when the ground subsided because of the torrential rains.

The train had to stop on the tracks overnight near the town of Tonneins, and the more than 500 passengers were evacuated by bus.

According to the prefecture, the rescue operation involved dozens including firefighters, police and volunteers.

"We narrowly avoided a disaster, the tracks were exposed and the TGV was suspended," the mayor of Tonneins, Dante Rinaudo, told AFP.

Describing "avalanches of water" in the town that flooded cellars and houses, he said the storms should be recognised by the government as a natural disaster.

Another train travelling between Toulouse and Paris was also stranded overnight in Agen, and passengers were taken to Toulouse by bus on Tuesday morning.

A spokesperson for the state rail operator SNCF said traffic would be suspended for "at least several days" between Agen and Marmande in southwestern France, affecting TGV services between Bordeaux and Toulouse.

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