The banging of wagons in a "domino effect" made the house shake and it was soon followed by screeching metal.

"It sounded like a jet going over the house," the Braidwood Road resident said.

"It came into my mind - 'what if a train derailed?'"

It was only the next morning she discovered that's exactly what had happened.

One of the five containers dislodged from the Brisbane-bound freight train stood precariously tilted on the tracks just three to four metres from her fence.

"It was a shock. If it had been any closer it would have been through the house," Miss Cosgrove said.

That was at about 2.30 to 3am Sunday. A major salvage and repair operation has been going on ever since on the main line just south of Goulburn Railway Station. Five containers on the super freighter, which was carrying retail freight such as beverages and dry goods, were damaged.

A spokesman for the Australian Rail Track Corporation said an internal investigation into the cause was underway. It is working with the Australian Transport Safety Bureau and the NSW Office of Transport Safety Investigations.

"Repair and recovery works are continuing on the north-bound track utilising different crane sizes and other machinery," a spokeswoman said on Monday.

" (It involves) clearance of the wagons away from the operating railway line and then repair of the track and turnouts (which allow trains to move from one track to another) as well as associated signalling works.

"The teams are building track panels - essentially pre-preparing the track while the wagon recovery is underway, to then drop them into place in replacement of the damaged track that's there currently. We will then top up the ballast and compact it around the track."

ARTC hoped the track would be cleared by late Monday or early Tuesday.

The line was closed on Sunday due to the derailment but the southbound lane re-opened just after midnight. It enabled northbound and southbound services to resume although train services were running at reduced speed. Crews worked well into the night under spotlights.

Meantime, there's been a steady stream of locals watching and photographing the salvage operation.

Several doors up, Miss Cosgrove's auntie, Ann McCrossin has been watching all the goings on. She is partially deaf but said she felt her house vibrate.

"The trains come through like lightning so something like that was inevitable," she said.

It's not clear at this stage whether speed was a factor in the derailment.

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