South Africa's gold miners have downed tools after last-minute talks over a wage row failed to halt strike action.
South Africa is the world's biggest producer of gold bullion
Around 100,000 members of the National Union of Mineworkers (NUM) began the walkout at 1600 GMT on Sunday.
Unions, who are demanding a 12% wage increase, rejected industry offers of a 4.5%-5% wage rise plus bonuses linked to a rise in the domestic gold price.
NUM General Secretary Gwede Mantashe told Reuters a number of offers had been made but "were not good enough".
Before the action began, Mr Mantashe said talks with individual companies were planned for later in the day, but warned that even if an improved offer was tabled, it would be too late to call off the strike.
"We are very aggressive in engagement when there's a strike as a union, because to us, the sooner you resolve the issues, the better it is for everybody," he added.
Earlier, Mr Mantashe had been locked in talks with the Chamber of Mines, which negotiates on behalf of gold producers.
Following the discussions, the chamber's head negotiator, Frans Barker, warned all new offers would be "off the table" if the action went ahead.
The strike is the first to affect the industry for 18 years.
South Africa is the world's biggest producer of bullion - accounting for around 15% gold output - and the sector accounts for approximately 8% of the country's gross domestic product.
Industrial action is expected to cripple production in South African mines belonging to three of the world's biggest gold producers - AngloGold Ashanti, Gold Fields and South Deep.
One analyst at Deutsche Securities has estimated that the action will lead to the loss of approximately 28,000 ounces of gold production and 79 million rand ($12.21m; £6.8m) in lost revenue per day.