The National Union of Mineworkers in South Africa announced that eight of nine gold miners trapped underground at the Doornkop mine west of Johannesburg had been found dead.

The union said the bodies had been discovered on Wednesday night by rescue teams. A search was ongoing for the missing ninth man.

Seventeen workers were initially trapped underground after a fire broke out over a mile beneath the surface at mining firm Harmony Gold's Doornkop operation late on Tuesday.

The accident appears to have been triggered by a seismic event, possibly an earthquake, which caused a rock fall to damage electric cables.

Eight workers were rescued on Wednesday morning after escaping to a refuge chamber.

NUM health and safety official Erick Gcilitshana said the blaze had still not been put out morning, although it was under control.

A 2.4-magnitude seismic event triggered the chain reaction that led to the blaze,
the union announced on Wednesday.

"It resulted in the collapse of underground rocks which caused damage to ventilation pipes, electric cables and water pipes," the union said.

The Department of Minerals and Energy called the disaster "deeply regrettable" and promised an investigation.

"We must ensure that we do all we can to get to the bottom of what caused this incident, in order to prevent similar occurrences in future," said Mining Minister Susan Shabangu.