The 955 mine workers who spent more than a day trapped underground in Sibanye Gold's Beatrix mine in South Africa following a power failure are all safely back on the surface.

A severe storm on Wednesday night collapsed power lines supplying the mine, located in South Africa's Free State province, and caused a surge and outage at all three of the shafts, Sibanye said in a statement on Friday. As a result, most of the Wednesday night shift couldn't be lifted to the surface.

While the workers at two shafts and were hoisted up using emergency back-up generators, damage to some equipment at another shaft meant that almost 1000 workers trapped there had to remain underground, the company said.

Power was fully restored to mines in the area at 1.40am, Khulu Phasiwe, the spokesman for state-owned utility Eskom Holdings SOC, said on Twitter.

Mine safety is a perennial concern in South Africa, which operates some of the world's deepest and most dangerous mines. 

Workers are having to go deeper in ageing shafts to access additional ore in a country that's been mined commercially for over a century.

Last year, fatalities in the sector increased for the first time in a decade.

Mineral Resources Minister Mosebenzi Zwane would visit the site for a briefing, his department said.

Sibanye expects to resume operations at Beatrix on Monday.

The company rose 2.3 per ent by 9.46am in Johannesburg, making it the third-best performer in a Bloomberg Intelligence index of 15 large gold companies.

Bloomberg