Winding gear at a giant South African platinum mine failed sending an elevator into a precipitous fall that killed 11 workers and injured 75, the operators said Tuesday.

Impala Platinum said 14 of the injured workers remained in "critical condition" after the disaster on Monday as the elevator brought the miners up after the end of their shift.

All operations at the Rustenburg mine, northwest of Johannesburg, have been suspended while an investigation is started, company chief executive Nico Muller said in a statement.

Muller said the "devastating accident" at the mine was "the darkest day in the history" of the company, which is known as Implats.

There were 86 employees in the three-level lift when it "unexpectedly reversed direction and began descending back down through the shaft," Implats said in the statement.

- 'Emergency' failure -

South Africa has the world's deepest mines and many have lifts that can carry more than 100 people at a time.

Implats spokesman Johan Theron told AFP that a winder mechanism at Rustenberg went into reverse and accelerated, causing the lift to plunge at speed.

One "emergency" system failed to stop the lift which came to an "almost instantaneous" halt when a counterbalance weight rose to ground level and was caught in safety devices.

Implats said the lift sped down for about 180 metres of the 1,000 (3,280 feet) metre shaft.

Theron said some workers were severely injured, most suffered from ankle and leg fractures. Others walked out with minor scratches.

Implats said the lift safety mechanisms "are used in mining operations globally. The failure of the arrest safety protocol is therefore unusual, highlighting the tragic nature of this accident."

"Implats is offering ongoing support to the families and colleagues of those lost in service," said Muller.

"We also hold our injured colleagues in our thoughts at this incredibly difficult time."

But trade unions questioned safety measures at the mine.

"This incident ... raises a lot of questions about health and safety issues," the National Union of Metalworkers of South Africa said in a statement.

Geoffrey Moatshe, of the National Union Of Mineworkers, said that shaft lifts need to be checked on a regular basis.

"If this thing was checked and maintained, this could have been avoided," Moatshe told AFP.

Mining employs hundreds of thousands of people in South Africa -- the biggest exporter of platinum and a major exporter of gold, diamonds, coal and other raw materials -- and accidents are common.

Dozens of mineworkers are killed each year, though numbers have been falling as safety standards have been stepped up over the past two decades.

More than 430 coal miners were killed in just one disaster in 1960 at Coalbrook. There were about 50 mining deaths in 2022, according to government statistics.

Industry group Minerals Council South Africa said 41 miners have died since the beginning of this year.

Implats said in August that five employees had died at work in various mines in the previous 12 months.

"This is a tragic accident. It serves as a stark reminder that there can never be any lapse in focus and vigilance regarding safety on mines," said Japie Fullard, head of a Minerals Council's safety initiative.