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Three people were killed and several others seriously injured when a tunnel collapsed at Eskom's Ingula pumped storage scheme near Ladysmith on Thursday morning.
Lieutenant Jack Haskins, of the police's search and rescue unit, said he understood three people had been killed and that five or six people were seriously injured.
A further nine people could not be accounted for.
The scheme, which is under construction, is expected to go live next year and involves pumping water up the Drakensberg Mountains from the Braamhoek Dam to the Bedford Dam during off-peak hours, an elevation of about 470 metres.
Water would then be released through the tunnels to flow down during peak hours, generating electricity.
