The death toll is thus rising, as witnesses earlier on Wednesday said that at least 60 people had died.
"We don't know how many more are still inside," one of the survivors told AFP.
Around 50 people have been injured in the accident, with the search for more victims being carried out using rudimentary methods.
Shafts in the mine in southern Sudan began to collapse on Tuesday.
The RSF is one of the warring parties in the Sudanese civil war, where the militia group is fighting the central government's army.
