Grand Central say the Kings Cross to Sunderland service is being disrupted after a body was found on the line.
The company said: "Due to the emergency services dealing with an incident The 11.27 London Kings Cross to Sunderland will terminate at Hartlepool.
"Grand Central apologise for the inconvenience caused by the delay and potential cancellation of your service today."
It said passengers going to Sunderland should travel on the 16.03 Northern Rail service from Hartlepool towards Carlisle.
It is believed the disruption has been cause due to a body being discovered on the railway line between Stevenage and Peterborough.