Firefighters are tackling a blaze on board the Caledonian Sleeper at Cupar station in Fife.
The Scottish Fire and Rescue Service was alerted to the incident in one of the carriages of a train on the Highlander route between London and Aberdeen, Inverness and Fort William.
Three fire engines went to the scene when the alarm was raised at 05:46 on Wednesday.
There are no reports of any casualties.
ScotRail said the incident was
disrupting its services between Edinburgh and Arbroath as no trains were able to run through the area.