South African state logistics group Transnet expects coal transported along its lines to triple to 30-million tons within seven years to meet demand at coal-fired power stations, a presentation showed on Tuesday.

"Indications are that the demand for the transportation of coal to Eskom's power stations will grow from 7-million tons currently to 30-million tons by 2019," Transnet said in a submission to Parliament.

Transnet is spending billions of dollars to upgrade its rail haulage system, where years of underinvestment is blamed for constraining exports of key commodities, including coal, iron ore and manganese.

Transnet has said it expects to transport at least 73-million tons of coal through the Richards Bay Coal Terminal in the current financial year to end-March, up from 68-million tons in the last financial year.