A train carrying milk 400,000 litres of milk for processing from Oringi, near Dannevirke, to Longburn, near Palmerston North ran into a landslide in the Manawatu Gorge.
Fonterra says the tankers were not de-railed, no-one was harmed and no milk lost as a result of the collision.
KiwiRail says the area where the slip occurred is difficult to access, and it will take several days to clear.
Further north, another freight train ran into a slip near Taumarunui on Saturday morning.
KiwiRail says the engine driver emerged safely from that train as well and the slip was cleared by Sunday.