The National Union of Mineworkers (Num) says it believes more miners are trapped underground at Harmony's Target Mine in Welkom than what the company claims.

Two people were killed and two others injured after a ground fall on Monday.

The two injured were treated in hospital.

Harmony?s Marian van der Walt said workers were going to continue searching the area to ensure no other miners were trapped.

"Until such time that the area has been made safe, until all the rocks have been removed and until such time that we have enough comfort that no more bodies are trapped under the rocks," she said.

However, Num's Lesiba Seshoka believes more people were affected than the company claims.

"We have not forgotten that just recently when hundreds of mineworkers were actually underground and 80 were found dead in what they call criminal mining," he said.