One person was killed and two more were missing after a charter boat on a popular sight-seeing trip capsized off South Africa's Hout Bay near Cape Town, rescue officials said on Saturday.

Two of those rescued from the twin-hulled catamaran "Miroshga" were French women, said Craig Lambinon, spokesman for the National Sea Rescue Institute. The boat was carrying 41 people, including crew, at the time of the accident, he said.

"We recovered one person out of the hull, who has been hospitalised in a stable but serious condition," Lambinon said, adding that rescuers were trying to free another two under the hull.

It was unclear what caused the boat to capsize in the cold waters close to Duiker Island, about three km from Hout Bay on the Atlantic Ocean side of the Cape Peninsula.

The island is a popular destination for tourists eager to catch a glimpse of thousands of seals found there.

Local media had previously reported that at least four people had died.

-Reuters