Nov 30 (Reuters) - South Africa's state-owned rail and ports firm Transnet said on Thursday it will add 14 extra trains a week to its main coal export corridor, nearly doubling capacity as it battles to move the fuel to ports for export.

Transnet said in a statement that more trains would be added between December and March 2024, which could help companies including Thungela Resources, Exxaro Resources , Glencore and Seriti that are struggling to move coal to ports due to insufficient rail capacity.

The company plans to add seven trains a week on the coal line by mid-December, from 21 a week. Another seven would be added by March next year, bringing the total to 35 a week.

More locomotives have become available due to repairs which are being carried out, Transnet said.

Transnet is struggling to haul bulk commodities to ports due to a shortage of locomotives and spares, as well as cable theft and vandalism to infrastructure.

This is costing mineral exporters billions of rand in potential export revenues and mining groups have resorted to trucking coal to Richards Bay Coal Terminal (RBCT) for shipments to markets including Asia.

Efforts to tackle cable thefts are improving and Transnet said it is reinstalling signalling equipment on the network.

Exxaro said on Wednesday that Transnet had transported 39.43 million metric tons of coal to the RBCT between January and October, equivalent to an annualised run rate of 47.44 million tons, which is below last year's 50.35 million tons and a record low in 30 years. (Reporting by Nelson Banya; Editing by Alexander Smith)