Transnet said no serious injuries were reported after the accident, but the disruption to South Africa's major coal export terminal at Richards Bay will throttle mineral shipments already constrained by locomotive shortages as well as rampant cable theft and vandalism of infrastructure.
The state-owned firm in an emailed response to Reuters did not provide details of what caused the accident and when service would be restored on the coal line.
Major coal exporters Thungela Resources and Exxaro Resources did not immediately respond to queries about how the derailment was affecting haulage to port. Glencore, another major coal exporter from South Africa, declined to comment.
Transnet has struggled for years to haul commodities to ports due to equipment shortages and maintenance backlogs after decades of under-investment.
This has forced companies such as Thungela and Africa's biggest iron ore exporter Kumba Iron Ore to cut production due to limited capacity to transport commodities via rail to port.
Some miners have been moving coal to port by road, a more expensive and environmentally damaging option than rail, but Transnet - which also operates South Africa's ports - in November announced curbs on trucks going into the Richards Bay port, citing "unprecedented congestion" on the coastal town's roads.
(Reporting by Nelson Banya; editing by Barbara Lewis)
