"Rescue workers are talking to the trapped miners, but we are not sure of their condition," Captain Cherelle Ehlers said.

A disused tunnel in the mine collapsed, trapping the men who were digging illegally for diamonds. Eleven managed to escape and alerted police that there were people underground.

"The miners are trapped in tunnels at the Bontekou mine in Kleinzee," said Ehlers. The mine closed the tunnels in April.

Police and rescue teams from Kommagas, Kleinzee, Port Nolloth, Upington, and Kimberley, as well as rescuers from the De Beers mine and the Nama Khoi disaster management were are at the scene. It is thought the tunnel collapsed at about 3am on Tuesday. The area that caved in was about six metres deep and led to several tunnels and an underground waiting area.

Three of the 11 who escaped were admitted to a hospital in Springbok.

Ehlers said loose gravel was hindering rescue efforts.