Two men have been trapped for more than an hour after descending into a mine on Stanley road in Primrose in Germiston, East Rand, on Thursday afternoon, paramedics said.
The owner and one employee of the mine had descended more than 75m into the mine to check on water levels, ER24 spokesperson Annine Siddall said.
Siddall said paramedics arrived on scene at 15:00 and found one of the men had run out of oxygen.
"Fire and rescue arrived on scene a few minutes ago. We are not sure what their condition is at the moment."
Local authorities have been called to the scene.