South African freight rail operator Transnet plans to reopen the first of two coal lines to the country's major coal export terminal on Thursday after it was blocked following a train collision last weekend, the company said on Wednesday.

The second line is expected to be operational by Saturday, Transnet said in a statement.

The two lines to Richards Bay, South Africa's main coal export port, have been out of service since Sunday morning after two trains collided, hitting mineral shipments already constrained by locomotive shortages as well as rampant cable theft and vandalism of infrastructure.

Transnet said although efforts to clear the tracks have been impacted by heavy rainfall in the region, it hopes to remove the remaining debris by Thursday morning.

"The rail service is expected to resume before midnight on Thursday, 18 January on Line 2, and on Saturday, 20 January, on line 1, subject to the weather conditions," Transnet said.

Coal miners Thungela Resources and Exxaro Resources both said they did not expect the derailment to significantly impact their exports of the fossil fuel. Glencore, another major coal exporter from South Africa, declined to comment.

The miners have for years struggled with Transnet's limited capacity to haul commodities to ports due to equipment shortages and maintenance backlogs after decades of under-investment.

Companies such as Thungela and Kumba Iron Ore, Africa's biggest iron ore exporter, have been forced to cut production to match Transnet's constrained capacity to transport commodities 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.