South Africa's gold miners begin strike over pay
Almost 100,000 gold miners have begun an indefinite strike in South Africa calling for a 14% salary increase.
The stoppage could cost the gold mining sector $25m (£15m) a day in lost output, economists say.
The National Union of Mineworkers (NUM) told the BBC it would affect all the top gold producers who are only offering between 7% and 9% pay rises.
The coal and petrol sectors have also been hit by strikes leading to fuel shortages in the last three weeks.
The BBC's Pumza Fihlani in the commercial capital, Johannesburg, says this time of the year is known as South Africa's "strike season".
Most unions are demanding salary increases twice that of inflation - which currently stands at 5%.
They argue that any reasonable increase in wages needs to be 11% to counteract price hikes in food, water, electricity and petrol over the past year.
NUM spokesperson Lesiba Seshoka said workers would down tools indefintely from the start of the night shift on Thursday at 18:00 local time (16:00 GMT) in all gold mines, including AngloGold Ashanti, Gold Fields and Harmony Gold.
"Our members work under dangerous conditions in the mines daily and yet they have nothing to show for it," Mr Seshoka told the BBC.
The average mine worker earns 3,800 South African rand ($570; £346) each month, according to NUM.
For decades gold mining was the backbone of South Africa's economy, but gold output has decreased in recent years.
Until 2007 the country was the world's largest gold producer, now it is fourth.
The decline has been attributed partly to an increase in labour costs.
According to the most recent World Economic Forum report on Global Competitiveness, South Africa had the eighth-highest level of industrial conflict of out of 139 countries.
A public sector strike over pay paralysed schools and hospitals for more than a month last year.