Martin van Breda, 54, his wife Teresa, 55, and son Rudi, 22, were found dead at their home on Wednesday at De Zalze Winelands Golf Estate, an exclusive golf resort in Stellenbosch, about 50km east of Cape Town, it has been reported.

Daughter Marli, 16, is in a critical condition, while another son, Henri, 20, was slightly injured.

South African media have reported the victims were killed with an axe.

"What I can say is they were not shot - the patients were axed. The daughter was rushed to hospital with severe head trauma and a severed jugular," emergency medical services spokesman Robert Daniels said.

"The other son had minor bruises on his arms. He was treated at the scene."

No arrests have been made.

The Times Live is reporting that Henri, was seen being "taken away" from the scene by police for questioning.

"[Henri] could not have been seriously injured because he could walk. I saw this myself,"  Eben Potgieter, chairman of De Zalze Winelands Golf Estate's home owners' association, told The Times.

"Henri is being treated as a witness at this stage. He had scratches and cuts."

The family reportedly lived in Perth for six years before returning to South Africa last year.

Martin van Breda was managing director of the Australian franchise of Engel & Völkers, an international company that sells and rents "premium residential property, commercial real estate and yachts", according to its website.

Engel & Völkers is based in Buderim, Queensland.

In a statement issued by Engel & Völkers in 2010, according to The Times Live, Breda is quoted as saying: "I am looking forward to opening up the Engel & Völkers network and providing its services to the Australian market. The demand for premium properties and a professional service provider is very high, especially here on the East Coast."

AAP