A British expat is believed to have been attacked by a shark while swimming off the coast of Cape Town in South Africa.

The 42-year-old is understood to be an expat who had lived in Cape Town for several years.

He reportedly lost most of his right leg and part of his left foot after being repeatedly bitten by the Great White.

Several beaches along the city's False Bay coastline this afternoon remained closed after officials warned it was likely the deadly beast remained in the area.

Craig Lambinon, a spokesman for the National Sea Rescue Institute, said the victim was this afternoon in a serious condition in a private hospital in the city.

"This man was swimming around 50 metres from the beach when the shark attacked him at around 12.20pm," he said.