A passenger train derailed at KiwiRail's Masterton yard this afternoon as it was travelling to the station to collect passengers.
The locomotive and part of a passenger carriage derailed, but no passengers were on the train at the time.
KiwiRail's acting chief operations officer Henare Clarke said the cause of the derailment is not yet known.
"Re-railing the locomotive may take some time as it will need to be lifted by crane. It is hoped this can be completed tomorrow to allow services to resume," he said.
Buses replaced the usual Wairarapa Line service between Masterton to Wellington this afternoon.
The region's train operator, Transdev, said trains will operate as normal tomorrow morning from Renall Street Station, one stop after Masterton.
A bus service will be put on between the two stations.