A LOAD shift has been identified as the likely cause of a freight train derailment near Nambucca Heads last year.

The Australian Transport Safety Bureau this week released a report into the May 14 crash which caused thousands of dollars in damage to the main line and other track infrastructure.

The fourth wagon from the northbound 3WB3 train derailed during the crash while travelling through the Nambucca Heads crossing loop.

The investigation found that prior to the crash the train's load likely shifted to the left, causing the right-hand wheels to unload from the track.

The Pacific National train travelled for a further 1.4km passing bridges and reaching speeds of 44kmh before the wagon tipped on its side causing the train to separate between the fourth and fifth carriages.

As the wagons parted, the train brake pipe separated, bringing the train to a stop 320m further down the track.

The left curve of the track likely resulted in more force from the wagon's right side to the left side, resulting in a further unloading of the right-hand wheels.

No one was injured in the incident but the line was closed for repairs until May 16.

The report said the ability for a load to shift is an undesirable condition that can affect the dynamic of rail vehicles.

"All rail freight operators should consider the safety implications of shifting/moving loads and should ensure that all loads are restrained and enclosed in a way that prevents movement in any direction relative to the wagon," it said.

The full report can be found on the ATSB website.