Two participants in the Ironman competition taking place in Port Elizabeth died on Sunday - one of a suspected heart attack while the other is believed to have suffered convulsions.

"It is with great sadness that we confirm the death of two race participants at the Ironman African Championship. Both athletes required medical attention during the swim portion of Sunday's race and were transported to a nearby hospital where they were treated," organisers said in a statement on Facebook.

"Our condolences go out to the family and friends of both athletes, whom we will continue to support. We are working with the local authorities to gather all details."