Five wagons have derailed from a northbound freight train at National Park in the central North Island.
KiwiRail said it understood one of the wagons has tipped off the track.
The train is blocking the Fisher Road level crossing, and other freight services on that line.
KiwiRail said its engineers were working to clear the site.
It said it was too early to say what caused the derailment, but it will be investigating.