South Africa's National Union of Mineworkers said on Tuesday that a seismic event had rocked DRDGold's troubled Blyvoor mine west of Johannesburg, which the company is trying to sell to a Chinese investor.

The union said in a statement that five workers had been injured and some had been taken by helicopter to hospital.

Company officials were not immediately available for comment.

DRDGold in June suspended financial assistance to Blyvoor, a deep-level mine in which it has a 74 percent stake, and launched business rescue proceedings to save it as its production declines and costs climb.