The Australian Rail Track Corporation, which operates the Hunter Valley freight rail tracks, said yesterday that both lines remained blocked at the accident site at Whittingham, on the Newcastle side of Singleton.

Both lines were likely to stay shut until at least tomorrow night while damage to the tracks was repaired.

The derailment is likely to leave Newcastle's coal-loaders short of coal because the coal tracks had only just reopened from a planned, four-day maintenance shut-down when the derailment occurred.

The corporation's "possession" of the rail tracks had been timed to finish at midnight on Friday night and the empty grain train came off the tracks about 9.30 on Saturday morning.

The majority of the Hunter's export coal comes from mines west of Whittingham, and a spokesman for Port Waratah Coal Services said the accident had resulted in a substantial impact on exports although the final cost would be "better understood towards the middle of the week".

The Port Waratah spokesman declined to put a dollar cost on the delays but an average daily throughput on recent tonnages and prices, two days shipments to the port would be worth more than $50 million.

A Hunter Valley police spokesman said the 28-carriage wheat train, travelling north, was derailed at a set of points about 300 metres north of Range Road.

He said both of the train's diesel engines and six of its wagons were at least partly derailed.

The engines and some of the carriages rolled.

The driver was taken to Singleton Hospital with minor injuries.

Firefighters were required to mop up spilt diesel that leaked onto the track.