HARARE, Zimbabwe (AP) — Some 20 miners are trapped underground after a mine shaft collapsed in Zimbabwe, state media reported Thursday, and a police spokesman said at least two bodies had been recovered.

Spokesman Paul Nyathi said the miners have been trapped since Wednesday when they entered for the night shift at the gold mine near Kwekwe city in central Zimbabwe. He said efforts to rescue the miners continue.

Police don’t yet know the exact number of trapped miners and other details, he said. The state-run Herald newspaper said at least 20 were trapped, citing officials at the scene.

The incident only came to light after the miners did not emerge on Thursday morning after their shift, the Herald reported.

Mining has grave risks in the southern African nation. It is often carried out by ill-equipped artisanal miners who sometimes invade abandoned mines. They are often trapped underground.

In February of last year, dozens of artisanal miners were trapped after tunnels flooded. Twenty-four bodies were later recovered and eight people rescued. Fears remained that many others remained underground because the unregulated nature of the mining made it difficult to account for everyone.