Eleven workers at a South African platinum mine have been killed and 75 others injured after a lift bringing the workers back to the surface dropped about 200 metres (656 feet), according to the mine’s operator.

Impala Platinum said the “serious accident” happened on Monday in the late afternoon at its mine in Rustenburg, northwest of Johannesburg, as employees were leaving one of the shafts at the end of their shift. The company said 75 workers were injured and were transferred to local hospitals and admitted for treatment.

Implats spokesman Johan Theron told the AFP news agency some were severely injured, most suffered from ankle and leg fractures, and others walked out with minor scratches.

The accident happened shortly before 5pm (15:00 GMT) on Monday as the lift hoisting employees “unexpectedly started descending”, according to the company. “Its rapid descent was stopped by the conveyance counterweight becoming trapped by the jack catches,” it said in a statement