Virgin Trains is warning of potential alterations and delays to its services between Rugby and London Euston.
The company has said that a person was hit by a train between Rugby and Milton Keynes Central stations, leading to trains being unable to run on some lines.
Virgin Trains is still running services, but is warning these may be diverted via Northampton on the slower line before rejoining the main line to get to Milton Keynes. Disruption is expected until 5pm.
A spokesman for British Transport Police said: "At 2.28pm today (29/08) officers were called to the railway lines close to Blisworth, Northamptonshire, following reports that a person had been struck by a train.
"Officers attended the location alongside paramedics, 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.”