The incident took place Wednesday afternoon, causing a ground fall in an operating stope at the mine, with 13 mineworkers unaccounted for.

Mine rescue teams were immediately sent out and three employees located Thursday.

It confirmed Friday that rescue teams had freed 10 of the 13 trapped mineworkers, with four having succumbed to their injuries and six in hospital.

Another employee had been located, but two remained unaccounted for Friday morning.  

"Management of Sibanye-Stillwater wishes to express its sincere condolences to friends and family of the four deceased employees," the company said.

It thanked the rescue teams and said every effort was continuing to locate missing employees.

The Department of Mineral Resources and unions had been informed of the event Thursday and had representatives on the site assisting with the rescue efforts.

According to an update by the National Union of Mineworkers Friday, one of the deceased was a NUM member.

"The NUM is angry and concerned at the rate at which mining incidents are happening at Sibanye-Stillwater," it said.

Minister of mineral resources Gwede Mantashe extended his condolences to the families and friends of the workers who lost their lives at the Driefontein operations.

"Greater attention must be paid to issues of mine safety and protection of lives, as opposed to the insistence of chasing production," he said.

Sibanye-Stillwater's has had a patchy safety start to the year, with it reporting in its March quarter operating results that there were three separate incidents at its South African gold operations in February, which fatally injured four employees.

One employee was fatally injured at the Driefontein operations on February 12 and two employees fatally injured at the Kloof operations on February 7. The fourth fatality was not specified.

At its South African PGM operations, two employees were also fatally injured in two separate incidents during the March quarter.

In January a power outage trapped hundreds miners underground at the Beatrix operations in the Free State province, although all were safely returned to surface.