JOHANNESBURG – The leader of South Africa's biggest platinum mining union on Friday threatened to bring Africa's top economy "to a standstill" and demanded a meeting with President Jacob Zuma, ramping up the rhetoric in an 18-month labour crisis.

The rand, which tumbled to a four-year low against the dollar on Thursday on fears of a strike at Anglo American Platinum (Amplats), extended its slide on concerns about further disruptions to an already struggling economy.

The currency fell as low as 9.43, its lowest since April 2009 when South Africa was still reeling from the effects of the US sub-prime crisis and the collapse of Lehman Brothers.

Joseph Mathunjwa, head of the Association of Mineworkers and Construction Union (AMCU), said Zuma's ruling African National Congress (ANC) was ignoring violence against its members in the platinum belt near the northwest city of Rustenburg.

"We are going to write another last letter to the office of the President that we need a meeting to talk about these issues at Rustenburg, of the killing of our members," he said on Johannesburg's Talk Radio 702.

"This is the show of AMCU's commitment to peace," he said. "We said we are going to bring the economy to a standstill."

AMCU's emergence since early 2012 as the most powerful platinum union had turned mining labour relations on their head, and sparked fears of a wave of industrial action stretching from the car plants of Durban to the vineyards around Cape Town.

The crumbling of the decades-long monopoly of the National Union of Mineworkers (NUM) had also opened the door to an array of worker committees and anti-capitalist activists opposed to the ANC and South Africa's post-apartheid economic status quo.

Faced with such a diverse and novel range of forces, the ANC appeared to be at a loss as to what to do, even though the decline of NUM - its ally in the decades-long anti-apartheid struggle - was likely to hurt it in an election next year.

"It's very difficult to decipher properly what is going on," ANC deputy president and NUM founder Cyril Ramaphosa also told the radio broadcaster.

"There's union rivalry, fighting for turf, and there are obviously other elements coming into the space. We keep hearing about the socialist workers party or whatever and that seems also to be fanning the flames," he said.

In the bloodiest episode of recent strikes, police shot dead 34 AMCU-linked workers at Lonmin's Marikana mine in August, the biggest loss of life at the hands of security forces since the end of apartheid in 1994.

An AMCU organiser was shot dead in a bar in Marikana at the weekend by unidentified gunmen.

AMCU members had also been implicated in the violence, including the killing of security guards and police last year.

Amplats Miners At Work

Despite threats from AMCU branch leaders, a strike at Anglo American Platinum, the world's top producer, failed to materialise on Friday, with all workers reporting for the morning shift without incident, the company said.

"Workers are going underground and there have been no incidents," spokeswoman Mpumi Sithole said. Amplats had announced plans to lay off  6 000 workers in a bid to return itself to profitability.

Amplats shares gained more than 2% from Thursday's eight-year low.

The dramatic slide in the rand - it had lost about 10% this year - was likely to stoke inflation, reducing the chances of the central bank rolling out a growth-boosting interest rate cut when it meets next week.

"The recent currency move is likely to keep it (the central bank) on edge a little, especially because it is only the start of what is likely to turn out to be a long, fraught and violent strike season," Nomura analyst Peter Attard-Montalto said.