Two children are feared missing at sea in different parts of the country.
Radio news reports said the search for the girl, off Mouille Point on the Cape Peninsula, involved two boats and a helicopter on Tuesday.
The National Sea Rescue Institute has since handed over the search to the police.
Meanwhile, on the other side of the country, off Port St John's in the Eastern Cape, a 15-year-old boy is missing after possibly having been attacked by a shark.
He had been swimming with several other people at second beach, where there has been a string of fatal shark attacks in recent years. – Sapa