Air and boat searches are underway for the remains of a swimmer who was attacked by a shark off Fishoek beach in Cape Town on Tuesday.

Eyewitnesses and lifeguards saw the man being dragged under the surf.

One woman said she watched the shark take an initial bite and then return.

“It then swam off, turned around very quickly and took the remainder of the body on his return and then he came out of the water and went off. Immediately there was a sea of blood,” she explained.

Flags alerting bathers to possible shark activity in Fishoek were hoisted earlier in the day.

The city’s Gregg Oelofse said it was impossible to spot every shark.

“When is it safe to go in the water and when is it not and when do we start closing the beaches every time there’s a shark, which means the beaches would be closed through the summer months. So it’s a very difficult thing to do and obviously it’s a very sad thing when somebody loses their life.”