South African freight logistics group Transnet said it may build a new rail line to the port at Richards Bay via Swaziland to free up capacity on its main coal export line.

Coal miners in South Africa have been unable to ship all their coal destined for exports due to lack of capacity on the rail lines linking their mines with the port.

"Transnet Freight Rail (TFR) is exploring the possibility of a new railway line through Swaziland to Richards Bay. The aim is to move general freight off the coal line," Sandile Simelane, spokesman for Transnet's freight rail unit, said in an email.

Business Day newspaper said that up to 15 million tons of non-coal cargo may be moved to the Swaziland line.

South Africa exported 63.4 million tons of coal last year, far below the expanded capacity at the Richards Bay Coal Terminal of 91 million tons. (Reuters)