A derailed freight train has been cleared from tracks near National Park in the central North Island.
One of the five rear wagons, which were mostly carrying frozen meat, tipped off the heat-buckled tracks just north of National Park about 4pm yesterday.
A number of freight trains and the Northern Explorer passenger train were unable to run until the line was cleared at 4.30pm today.
Freight services have restarted and the Northern Explorer tourist service will run tomorrow as normal.
KiwiRail group general manager of network Todd Moyle said earlier today the cause of the derailment was still unknown.
"We need to download data from the locomotive, complete measurements and assessments of both the track and the rolling stock and all that information will allow us to assess what the cause of that derailment was."
Mr Moyle said there was no significant damage to the track.
Investigators from the rail company said the freight train was moving extremely slowly when it derailed.
Trains must slow down when track temperatures go above 40°C.