Johannesburg - Eskom will brief the media on Friday about the accident at its Ingula pumped storage scheme in which six contractors died.
The platform they were working on collapsed in a tunnel at the construction site near Ladysmith on Thursday morning.
Eskom acting spokesman Andrew Etzinger said that seven others were injured.
Three were in hospital in a critical condition and four were discharged from hospital later in the day.
Etzinger said the tunnel in which the men were working was not damaged, contrary to initial reports of a tunnel collapse.
The men were doing welding and grouting on a platform in one of four tunnels.
“For some reason, the platform came loose and rolled down the tunnel.”
He described the platform as “a moveable vehicle which broke loose and rolled back” down the tunnel, which has a 24 degree incline. He could not say how far the platform fell.
Etzinger said all 3387 workers on site were evacuated and that the site would be shut until it was declared safe.
The briefing would be held at Eskom's Megawatt Park in Johannesburg at 10.30am. - Sapa