President Cyril Ramaphosa has sent his condolences to the families of four South African National Defence Force (SANDF) members who passed away while on duty overnight on Friday.

The four members were deployed to a mine in the North West and their lifeless bodies were found inside a container structure they had used as a guard house.

"As Commander-in-Chief of the SANDF, President Ramaphosa offers his condolences to the families of the victims as well as to their commanders and colleagues.

"The President's thoughts are with the team of soldiers who discovered their deceased colleagues in a container at a disused mine shaft at Orkney in the North West province," the Presidency said in a statement.

An inquest into the deaths has been opened by the South African Police Service.

"While police are investigating the matter, the deceased troops, who showed no injuries and were fully kitted and armed, are believed by the police and the SANDF to have died from carbon monoxide poisoning resulting from a fire they made to keep warm.

"The troops were part of Operation Vala Umgodi which is directed at combating illegal mining," the statement read.

In a statement at the weekend, the SANDF said the members were stationed on a 24-hour shift at Shaft 3, a dormant mining shaft in Orkney, North West, next to the abandoned Harry Oppenheimer stadium which has been a hotspot for illegal mining.