At least 14 people died on Thursday morning when a train collided with a truck, causing several carriages to catch fire.
A spokesperson for the health department in Free State, Mondli Mvambi, said heavy duty machinery was on its way to the scene on Thursday night, in an effort to find more bodies which might be trapped in the train's carriages.
The search for bodies is due to resume once the heavy duty machinery arrives, sometime on Friday evening or Saturday morning.
Several reports put the number of fatalities at 18, but but Eyewitness News (EWN) reported that this number could rise.
More than 250 passengers were reportedly on board, although there appears to be confusion about the total number of passengers and those injured.
BBC World News reported that at least 700 people were on the train, and that the number of those injured could be more than 268.
But Mthuthuzeli Swartz, acting CEO of Prasa, reportedly told AFP that it would be "tragic and unexpected" for the death toll to rise.
"The pathologists who are here have given us the assurance they are convinced that the number of the dead, 18, will be the final number." He told AFP there were 88 survivors in hospital.
According to EWN, the train was traveling from Port Elizabeth to Johannesburg, when it hit a train attempting to cross a railway. Transport minister Joe Maswanganyi told eNCA that the truck driver was "taking chances" by trying to cross the railway tracks. He is reportedly in a critical condition in hospital.
Families who are looking for loved ones who were on board the train can call 011 544 9623, and officials will be able to assist with tracking them down. Most patients have been transported to hospitals in Johannesburg.