KiwiRail says it expects the line through the Manawatu Gorge to remain closed until the end of the week while a slip is cleared.
The line was closed after a locomotive pulling a milk train derailed when it hit the slip on Saturday morning.
Contractors have been working since Sunday morning to clear the debris and move the locomotive.
In the meantime, KiwiRail says, it has arranged freight services for its customers, using alternative rail lines and road transport.
It says a site assessment shows that about 10,000 cubic metres of debris still needs to be moved so that a crane can be brought in to move the locomotive.
The Fonterra milk train was carrying 400,000 litres of milk from Oringi, near Dannevirke, to Longburn, near Palmerston North.