The train was derailed while heading south from the small town of Boggabri in Australia's coal-rich Hunter Valley to Newcastle port.
The closed section of the railway line is part of a larger network that feeds into the port, but a prolonged outage could boost Australian coal prices, which have been under pressure in recent months due to a global oversupply of the fuel, industry sources said.
"Initial indications are that significant damage has been caused to the bridge and the track - and comprehensive repairs will be required," ARTC said in a statement.
"As a result, there is currently no forecast or estimate to returning the track to service at this stage and the line remains closed."
An ARTC spokesman was not able to provide information on which mines were affected. Coal mines in the area include Whitehaven's Sunnyside and Tarrawonga mines and Idemitsu Kosan Co Ltd's Boggabri mine. (Reuters)