Police in Wellington are looking for passengers who used an emergency button to stop a commuter train and then vandalise it.
KiwiRail said a small group of passengers on the Tranz Metro Johnsonville line sprayed graffiti on the outside of a carriage before running off.
KiwiRail said it was appalled by the vandalism of public property, and by the upset it caused passengers and staff.
The cost of repairing the damage was estimated to be $6000.
The trains belong to Greater Wellington Regional Council, so KiwiRail was unable to comment in detail.
Police are reviewing security footage in a bid to find the culprits.