South African police have launched an investigation after 14 suspected illegal miners died when a mine dump site collapsed on them on Monday night.

Eight others were injured and "an unknown number... may still be trapped underground", police said in a statement.

The site was being legally operated by a mining company and it is unclear how the miners, most of whom are believed to be from neighbouring Lesotho, gained access.

Illegal mining is rife in South Africa as miners, known in South Africa as "zama zamas" ("those who try their luck" in Zulu), try to eke out a living by digging in abandoned shafts or dump sites.

Regional police chief Lt-Gen Arthur Adams, who visited the scene on Tuesday morning, said that the dump site was being used to mine platinum and other metals by a local company.

He told local broadcaster Newzroom Afrika that the "walls of the dumping site... caved in on them [the zama zamas]".

Adams said that three of the injured miners have since been released from hospital and have been detained by police.

He confirmed that all the zama zamas are undocumented foreign nationals and will also face illegal mining and trespassing charges.

Adams said the search continues for any miners who may still be trapped under the rubble.

"As it stands, the excavation operations have ceased," he said.

Injuries and deaths of illegal miners are not uncommon in South Africa, especially at abandoned mine shafts.

In January last year, 78 bodies were recovered from a disused shaft in Stilfontein, south-west of Johannesburg,

The miners had been stuck there following a nationwide police operation to end illicit mining at disused sites that had closed, as the industry – once the backbone of the country's economy – was shrinking.

It is no longer profitable for mining multinationals to operate in many places, but the promise of still finding gold deposits proves was a magnet for many desperate people particularly undocumented migrants.