South African gold producer Harmony Gold launched a rescue operation on Wednesday to free 17 miners trapped a mile underground by a fire and rock-fall at its Doornkop mine near Johannesburg.
The company said it had made contact with eight miners who had managed to flee to a refuge bay at a depth of 1,700 metres but the whereabouts of the remaining nine was unknown.
"The priority is simultaneously to get the fire under control and to reach the eight that are in the refuge bay and to find the nine who are still unaccounted for," Harmony spokesman James Duncan said.
"As far as we know the eight that are in the refuge bay are fine."
Emergency teams had been sent underground but were struggling to get to the area because of smoke and a subsequent rock-fall, he added.
Chief executive Graham Briggs cancelled a presentation he had been due to give at a major industry conference in Cape Town in order to fly to Johannesburg to oversee the rescue effort. Normal mining operations had been suspended.
South Africa's gold mines are the deepest in the world and ranked as some of the most dangerous during the apartheid years.
Since the end of white-minority rule in 1994 the government, unions and companies have worked hard to improve safety, but 112 people were still killed in the mines in 2012, the last full year for which records are available.
At least 82 men - thought to have been illegal miners - died after an underground fire at a Harmony mine in 2009. Most of the victims are believed to have died of suffocation.
All miners carry emergency oxygen packs and rescue bays are equipped with food, water and breathing equipment in the event of prolonged underground entrapment.