JOHANNESBURG (AFP) - Over 200 workers were feared trapped on Sunday inside an illegal gold mine in South Africa, emergency rescuers said.

"We have got communication with about 30 trapped miners. They have told us that underneath them there's 200 others," Werner Vermaak spokesman of private emergency operators ER24 told AFP.

But he said he could not independently confirm the figure of 200 and local municipality officials oould only confirm 30 trapped.

The workers went down on Saturday into the mine, dug illegally behind a cricket stadium in the Benoni district east of Johannesburg.

They failed to come out after a boulder fell and blocked their way, municipal rescuers said.

"We are currently in the process of attempting to rescue them," Roggers Mamaila of the Ekurhuleni municipality emergency services told AFP.

Heavy duty excavation equipment has been brought in to help in the rescue.

But Vermaak said it was "very dificult to access them at this moment".

Mine accidents are common in South Africa, both at legal and illegal operations.