South African mines producing half the world's platinum shut down on Thursday (January 23) as the sector's main union began a strike for hefty wage rises their employers say they cannot pay.

Members of the Association of Mineworkers and Construction Union , walked out at Anglo American Platinum, Impala Platinum and Lonmin, the top three producers of the metal used in jewellery and catalytic converters in cars.

The chief executives of the three companies have said the wage demands are "unaffordable and unrealistic" and warned the industry could ill-afford further production and job losses.

Implats closed its mines and processing units at Rustenburg, northwest of Johannesburg, before the strike began. It expects to lose about 2,800 ounces of platinum daily while smaller rival Lonmin estimates losses at some 3,100 a day.

AMCU has as many as 100,000 members in the platinum belt, 70 miles northwest of Johannesburg.

It was unclear if all AMCU members had heeded the call to strike but about 3,000 strikers gathered for a rally near Lonmin's Marikana on Thursday.

The government has offered to mediate to try to end the dispute, which threatens to further squeeze an already struggling economy.

President Jacob Zuma and the ANC want to end labour unrest before general elections due in about three months. But miners are angry about their lack of economic progress two decades after the end of apartheid.

The companies have indicated that they are willing to engage with AMCU and the union said on Thursday it had received a mandate from its members to participate in the talks.

AMCU had also planned to strike at several gold mines on Thursday but a court ruled the action be suspended pending a review of its legality.

Presented by Adam Justice