South African state-owned freight rail company Transnet said on Friday that repairs to a commodities export line had been significantly delayed by violence.

A train carrying coal for export derailed earlier this week on its way to the Richards Bay port.

Transnet said in a statement on Friday that there had been "violent extortion efforts" over the coal train derailment near Ulundi.

It added that it had implemented force majeure on the North Corridor rail route. In an effort to minimize the impact it is diverting some critical flows such as chemicals via the mainline between the port of Durban and the Gauteng province where the biggest city Johannesburg is located, Transnet said.

(With input from Reuters)