A train reportedly stopped at the level crossing after hitting a person in the Stannington Station area.
There is major disruption to the rail network, although the line recently re-opened.
A British Transport Police spokeswoman said: “Officers were called to Stannington level crossing at 8.16am this morning after reports a person had been struck by a train.
“Colleagues from Northumbria Police and the North East Ambulance Service are also in attendance, and sadly a person has been pronounced dead at the scene.
“The incident has been declared non suspicious, and inquiries are on-going.”