A fire at Harmony Gold’s Doornkop Mine left rescue crews scrambling to find to nine miners believed to be trapped in the deep mine that is west of Johannesburg.

According to a report from the BBC, eight other miners were successfully brought to the surface, following at rock fall that is believed to have been triggered by a fire in the mine on Feb. 4.

"Efforts continue to establish the whereabouts of a further nine employees who are currently unaccounted for," spokesman James Duncan told the BBC on Feb. 5.

The fire began about 1,700m (5,600 ft) below ground. Duncan said rescue teams were struggling to access the affected area because of smoke and rock fall.

It was unclear what started the fire, but Harmony Gold has confirmed there was some seismic activity in the area.

South Africa's National Union of Mineworkers says this resulted in the collapse of underground rocks which caused the fire.

The eight workers who were successfully rescued had managed to reach a "refuge bay", where there was compressed air and water kept for such incidents.

The incident came at the Mining Indaba Conference was being held in Cape Town under the shadow of a major strike that is crippling the nation’s platinum mining sector.