A fire and rock fall at South Africa's Harmony Gold's Doornkop mine near Johannesburg has left eight miners dead and one missing, the government said.
The incident is the most serious accident in South Africa's mines since nine workers died in a rock fall at a platinum mine in July 2009.
"The situation is deeply regrettable," Susan Shabangu, the mineral resources minister, said in a statement on Thursday.
"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."
The company said the search continues for the ninth employee.
Rescue teams worked through smoke and debris nearly a mile underground to reach eight other miners released on Wednesday.
Those miners, who were all unharmed, had fled to a refuge bay equipped with a telephone and other survival gear.
The National Union of Mineworkers said the fire broke out on Tuesday evening after an earthquake damaged ventilation and water pipes as well as power cables.
South Africa's gold mines are the deepest in the world and were ranked as some of the most dangerous during the apartheid era.
Since the end of white-minority rule in 1994, the government, unions and companies have worked to improve safety, but 112 people were still killed in 2012, the last year for which records are available.
Pay rise talks
The accident happened as platinum producers said that talks aimed at ending a crippling two-week-old strike by miners had broken down, with no date set for further negotiations.
Government-brokered talks with the Association of Mineworkers and Construction Union (AMCU) "have been adjourned as the parties have been unable to reach a settlement," three top producers said in a statement on Wednesday, according to the AFP news agency.
Criticising the AMCU for unwillingness to negotiate, the chief executives of Anglo American Platinum, Impala Platinum Holdings Limited (Implats) and Lonmin said the union's demand of a minimum $1,125 monthly wage was not feasible.
"Acceding to AMCU's demands - which have not shifted since negotiations began - is simply not feasible, and would effectively mean a doubling of the industry's wage bill," they said.
Employers had offered to raise salaries by a minimum of seven percent each year for three years.
Around 80,000 members of the AMCU downed tools on January 23.
Joseph Mathunjwa, the union's president, had hinted earlier on Wednesday that a proposal from independent mediators could provide a way forward.
The Commission for Conciliation, Mediation and Arbitration (CCMA) did not publish its plan.
"Once the employer concedes to the proposal of the CCMA, that would unlock the engagement to be taken to the next level," Mathunjwa said.
Mathunjwa vowed the stoppages would carry on until a deal was reached.
"We will continue the strike until the workers give us a mandate. They are still saying it is too early for them. They want the status quo to change."
Workers are outraged at rampant inequality in Africa's largest economy, and the high salaries of company bosses in proportion to other workers.
But the firms stressed such dramatic hikes were impossible, claiming the strike had already cost the South African economy $360m.
That claim could not be independently verified.
"Prolonged strike action will result in more losses, and a further restructuring of the platinum sector," the firms said.
South Africa's northern platinum belt has been the scene of work-related bloodshed since some 34 platinum miners were shot dead by police during a strike at Lonmin's Marikana mine in August 2012.
On Tuesday police said they used stun grenades and rubber bullets to disperse 3,000 "violent" striking AMCU miners.