JOHANNESBURG (AP) — Rescue efforts are underway in South Africa to bring 260 workers trapped in a gold mine for a day back to the surface, the Sibanye Stillwater mining company said on Friday.

According to the company, an initial investigation showed that a sub-shaft rock winder skip door opened at the loading point and caused some damage to the mineshaft at the Kloof mine, west of Johannesburg.

“Following a detailed risk assessment, it was decided that employees should remain at the sub-shaft station until it is safe to proceed to the surface, in order to avoid walking long distances at this time,” the company said in a statement.

The National Union of Mineworkers, which represents workers at the Kloof mine, said the miners have been trapped for almost 24 hours, with the company repeatedly changing the estimated time for them to return to the surface.

“We are very concerned because the mine did not even make this incident public until we reported it to the media,” said NUM spokesman Livhuwani Mammburu.

The company said all miners were accounted for and safe, adding that it expected to hoist them back to the surface on Friday.