Harry Potter rail line closed by 50-acre fire
Network Rail said the alarm was raised at 11:10am, 20 minutes after the Jacobite steam train had passed the location.
The route was closed at noon with disruption expected until 5pm.
The Scottish Fire and Rescue Service said firefighters and four appliances were tackling the 50-acre blaze, which has been brought under control.
West Coast Railways, which operates the weekday steam service, was unable to say yet whether the train had been involved.
A spokesman said: "We take this very seriously and have been taking additional precautions, which have included patrols following the train."
The route, including the Glenfinnan Viaduct, featured in the Harry Potter film series.