An accident at a platinum mine in South Africa has killed 11 workers and injured 75, the mine’s operator says.

Impala Platinum chief executive Nico Muller described it as the “darkest day” in the company’s history.

The firm said the accident involved a winding rope connected to a cage-style lift which hoists people up and down the mine shaft. The lift started moving downwards unexpectedly, it added.

South Africa has some of the world’s deepest mines.

It is a leading producer of platinum, gold and other raw materials.

There have long been concerns about safety conditions on its mines, but the situation has improved since white-minority rule ended in 1994.

The latest accident took place on Monday at a mine in Rustenburg, about 100km (60 miles) north-west of Johannesburg.

The deaths bring to 55 the number of fatalities on South African mines this year.

“This is a terrible blow to our ambition of ending 2023 with fewer fatalities than last year when there were 49 fatalities, the lowest on record, and the continuation of our journey towards zero harm,” said Mzila Mthenjane, the chief executive of Minerals Council South Africa, the main representative of mining firms in the country.

Mineral Resources Minister Gwede Mantashe has visited the mine.

He described the accident as a disaster, and said a thorough investigation would take place to establish what happened.

Impala Platinum said that operations at the mine have been suspended.

“Implats is offering ongoing support to the families and colleagues of those lost in service,” Mr Muller said in a statement.

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

Company spokesman Johan Theron told the BBC the surviving 75 mineworkers were all “injured to some degree” and sent to hospitals, but that some have “very serious” injuries.

He said 10 people were in a critical condition, with one airlifted to Johannesburg for “intensive care”.

The cage-style lift that was used to take workers out of the mine went into an uncontrolled fall and hit the bottom of the shaft, Mr Theron added.

Some of those affected by the tragedy were from outside South Africa, the company spokesman said.

Mr Theron was quoted by local media as saying the accident was “highly unusual”, and the lift was used worldwide and had a reputation of being safe.

Lifts in many of South Africa’s deep mines can carry more than 100 people, according to the AFP news agency.

The president of the Association of Mineworkers and Construction Union, Joseph Mathunjwa, told the BBC that the company “must take full responsibility and go beyond the normal tick-box exercise in terms of compensation” for the victims.

He said the 11 miners “perished underground due to the malfunctioning of the cage” and that “we believe strongly that this accident could have been avoided because already the signs were there that it was malfunctioning”.

Mr Mathunjwa said a malfunction was picked up during an earlier servicing of the lift but an investigation said it was in good condition.

When the BBC put the claim to the mining firm, a spokesman said they were not aware of the issues raised, but the union was welcome to come forward with its concerns.

Equipment was checked on a daily basis, the spokesman added.

Mr Mathunjwa said the union wanted an “independent expert” to be involved in the official investigation.

The National Union of Mineworkers of South Africa said the workers who died were not “just numbers”, but were bread-winners of families which loved them.

“This incident is gravely concerning and it raises a lot of questions about health and safety issues,” it added in a statement.