A SWIMMER who ignored a shark warning at a closed Cape Town beach lost his legs overnight when a great white attacked him, authorities said. The 42-year-old man entered the water at Fish Hoek Beach around 12:15 pm (8.15pm yesterday AEST), an hour and a half after shark spotters had seen the animal, raised a warning flag, sounded a siren and closed the beach, the city said in a statement. The man entered the water anyway, and before shark spotters could get him out, the great white attacked. His right leg was completely amputated and his left leg was bitten off below the knee, the National Sea Rescue Institute said. Although he has not been named, the institute said he was believed to be a British national living in South Africa. The man has been airlifted to hospital for treatment, the city said. "When the victim entered the water, the beach was still closed and the shark flag indicating the presence of a white shark was flying,'' the city said. Three nearby beaches have now been closed as the shark has still been seen swimming in the area, it added. The city's Shark Spotter programme monitors for sharks at nearby beaches to warn people when to leave the water. At least three sharks had been spotted during the morning.