French officials banned swimming yesterday off some of the Riviera’s best known resorts after several beachgoers reported a rare shark sighting in coastal waters.

Rescuers patrolling aboard an inflatable motorboat spotted a two metre long shark with a “stiff dorsal fin, gills and a white underbelly”, said Michel Gagnaire, head of public safety for the town of Cagnes-sur-Mer near the city of Nice.

Swimming has been banned off Cagnes and the neighbouring communities of Villeneuve Loubet and Saint Laurent du Var until at least today, even though shark sightings are rare off France, and attacks even more so.

Richard Chemla, head of the marine discovery centre in Nice, said it was either a basking shark or a manta ray.

“It’s perhaps a young shark that has approached our shores,” he said.

According to the Florida Natural History Museum’s respected “International Shark Attack File”, there has been only one fatal attack by a shark in French waters since their records began in 1847.

Mr Gagnaire said, however, that as the shark had been spotted in waters only 70 metres off the coast it may be disorientated due to illness or a wound and therefore more likely to attack swimmers.

In July last year another French Mediterranean beach, at Antibes, was closed after a shark scare, only for authorities to later discover the sighting had been of a large but harmless ocean sunfish, which eats jellyfish.