A mining company in South Africa says four workers have died and two others are missing after an earth tremor caused a rockfall at a gold mine.

The Sibanye-Stillwater company says 13 miners had been trapped at the Masakhane mine in Driefontein after the 2.2-magnitude quake on Thursday.

The company says six miners were rescued and one has been "located" in the mine.

A South African labor group is expressing concern over what it calls the "deteriorating safety record" at Sibanye-Stillwater facilities. Earlier this year, about 1,000 miners were trapped at another Sibanye-Stillwater gold mine for nearly a day after a power failure.

The Congress of South African Trade Unions says there have been more than 25 deaths in the country's mining industry this year.