A mass derailment of wagons laden with meat and byproducts near Palmerston yesterday morning closed the main south railway line and sparked an investigation.
The southbound freight train was hauling 20 wagons when it derailed on straight tracks between Palmerston and Bushey about 5am.
Nine wagons derailed, toppling on to their sides. A KiwiRail spokeswoman confirmed one container had burst.
The train had been carrying meat and a byproduct, bone meal, at the time of the incident, she said.
The train driver, the only person on board, was uninjured.
''Derailments can be caused by a number of factors and often a combination of differing factors,'' the spokeswoman said.
It was ''too early to speculate as to the cause'', but preliminary investigations suggested failings with a New Zealand-made wagon.
An official investigation was under way, she said.
A witness told the Otago Daily Times the engine and undamaged wagons resumed their journey south just before 10am.
A recovery operation was launched yesterday afternoon, with a crane attempting to right and re-rail the damaged wagons.
No decision had been made on where those wagons would be repaired, she said.
The derailment had caused significant track damage, and was expected to take at least 24 hours to repair, affecting about a dozen services.
KiwiRail had contacted affected customers so they could make alternative arrangements to freight their products, she said.
