Virgin Trains said: "Due to reports of a person being hit by a train at Northallerton, the line is currently blocked."
Multiple services have been delayed for several hours, including London to Edinburgh trains running on the line.
Replacement rail services have been organised between York and Darlington.
A spokesman said: "Replacement coach services have been organised to run between #York and #Darlington in both directions. Please speak to station staff for assistance."
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