For most of the year the Paillon is barely a river at all. It slips through central Nice largely hidden under roads and gardens before reaching the sea by the Promenade des Anglais, and homeless people often shelter in its dry tunnels. On Thursday, rain falling on the hills behind the city turned it into a fast brown torrent within a short time.

Shortly before half past two in the afternoon, a fire crew driving along the bank saw a man being carried off by the current. He was swept about 50 metres before managing to cling on in a recess inside the covered channel. A command post went up near the Palais des Expositions, swift-water rescuers and divers worked through the tunnels, and teams waited on the beach in case the worst had happened.

It had not. By the city’s count that evening, six people ended up safe: firefighters rescued or helped four of them, and two climbed out by themselves. The man first spotted in the water was treated for hypothermia at Pasteur Hospital. Mayor Éric Ciotti, who came to the scene to thank the crews, said he was unhurt but in shock.

The storm caused trouble well beyond the Paillon. Cannes and Mandelieu-la-Napoule had logged more than 130 millimetres of rain by early afternoon, flooding town centres and prompting school evacuations. A landslide shut the Lower Corniche near Èze, cutting the coast road to Monaco, while 22 homes were damaged by a slip in La Turbie and part of a roof collapsed in Grasse. Trains stopped running between Saint-Raphaël and Les Arcs.

Charles had already battered Madeira and mainland Portugal earlier in the week. Forecasters are keeping the department on its second-lowest alert level, with the sea still threatening low-lying stretches of shore on Friday.