British Transport Police confirmed they had been called to the railway close to Huddersfield following reports of a casualty on the tracks.
In a statement, they said: "Shortly after 1.45pm today (29/08) officers from British Transport Police were called to the railway close to Huddersfield, West Yorkshire after reports of a casualty on the tracks.
"Paramedics also attended, however a person was sadly pronounced dead at the scene. Officers are now working to identify the person and inform their family.
"This incident is not currently being treated as suspicious and a file will be prepared for the coroner."
Rail replacement buses have been sent to a number of stations, including Dewsbury, Huddersfield and Leeds, following the incident.
TransPennine Express tweeted that all lines between Stalybridge and Huddersfield had been blocked while emergency services responded to an incident.
Disruption was first reported shortly before 2.30pm today (August 29). All lines have now cleared, but disruption is expected to continue until at least 5pm.
As well as the replacement buses, tickets for disrupted services will also be accepted on alternative routes. Click here for more information.