Cape Town, Jun 24 (IANS): At least 31 suspected illegal miners were believed to have died at an old mine in the Free State province of South Africa, authorities said.

The miners, believed to be from Lesotho, died on May 18 in a mine ventilation shaft that was last operational in the 1990s, the Department of Mineral Resources and Energy said on Friday in a statement.

It said that dispatching a search team to the shaft would be too risky, as current methane levels at the mine ventilation shaft remain high, Xinhua news agency reported.

South Africa was informed by the Lesotho government about the deaths, the statement said.

The department is considering various options to "speedily" deal with the "unique and strange situation," the statement added.

"All relevant stakeholders will endeavour to ensure that the suspected deceased illegal miners are brought to the surface," it 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.