A fire at Groenpunt Prison, in the Free State, was part of an elaborate escape plan, the correctional services minister said.
Correctional Services Minister Sbu Ndebele said maximum security inmates set the blaze after an initial escape attempt, according to a report in the Sunday Times.
"They started with the locks and then broke the beds and made keys and weapons. They started there and moved and lit the fires," he said.
Six jail cells and three administration offices were gutted by the blaze and all files on the inmates were destroyed.
Ndebele told the newspaper the timing of the riot was planned. "There is a mistaken idea in the prison ... that, during Christmas, we are relaxed and most attempts to escape come then.
"They will be shocked, because we know all about that."
He said that his personal experience of being a prisoner meant that he understood "both sides very well".
According to the report, some members of prison staff could be suspended for failing to avert the riot.
Four prison warders were injured in the riot. About 50 inmates were injured when police moved in to stop the riot.
Prisoners had complained about the quality of food and about some prison officials. They also wanted a unit head to be fired. – Sapa