A South African miners' union says about 87 people are trapped after a building collapsed at a gold mine in the country's eastern Mpumalanga province.

A spokesman for the Association of Mineworkers and Construction Union, Manzini Zungu, said 52 people were trapped when an office building collapsed above ground on Friday, trapping an additional 35 miners below ground. Zungu said 80 miners have been rescued so far.

Zungu said the building collapsed in the town of Barberton Friday morning.

Television news channel eNCA reported the rescued miners had no serious injuries.