A train came off the tracks near Grange-Over-Sand in Cumbria, Northern has said.
All lines between Barrow-in-Furness and Lancaster are currently blocked.
Network Rail staff have been on site since in the early hours, the train company said.
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Ticket restrictions for other train operators like Transpennine Express and Avanti have been lifted, while road rail replacement vehicles have been requested, Northern said.
Northern advised people to reconsider their journeys and check before they travel.
This story will be updated as we learn more.
