South African authorities say they have been notified of the death of at least 31 suspected illegal miners, believed to be from Lesotho, at a disused mine in Free State.

South Africa’s department of mineral resources said in statement that it was informed by the Lesotho government about the deaths, on 18 May, in a mine ventilation shaft.

The mine in Welkom, Free State, was last operational in the 1990s, it said.

South Africa's mineral resources department says it has also been made aware that three bodies have been retrieved from the mine by other illegal miners.

It says it is doing its “utmost best” to act on this information and has been working with all relevant stakeholders, including previous owners of the mine, to retrieve the bodies.

It however says inspectors have assessed the situation and determined that the conditions there are too risky to send a team.

"[The] methane levels in the mine ventilation shaft 5 are very high. It is too risky to dispatch a search team to the shaft,” the department said.

Fatal incidents at old mines are not uncommon in South Africa, with illegal miners including migrants often risking their health and safety in abandoned shafts.