A 24-year-old surfer was fighting for his life in hospital after a shark bit off his leg off the French Indian Ocean island of Reunion Saturday, authorities said.

"The body boarder's right leg was severed at the thigh," the territory's local administration said in a statement. The incident took place around 20 metres (yards) from the beach.

The two other shark attacks reported off the island this year were deadly. The authorities said the latest victim, a local man, was outside the protected perimeter. They urged beachgoers to exercise the utmost caution.

Some argue that the growing amounts of wastewater poured into the sea attract sharks while others blame a marine reserve where fishing is banned for the spike in attacks in recent years.