Police confirmed the person was hit between Wigan North Western and Warrington Bank Quays, and all lines are currently blocked.
Olympic athlete Jenny Meadows, from Abram, was at the station at the time of the incident.
The world and European medallist tweeted: “Feeling heartbroken that a young girl has just taken her life in front of me at Wigan train station. If in need please speak out.”
Train services running through these stations may be cancelled or delayed by up to 60 minutes. Disruption is expected until 17:00.
A Northern Rail statement said: “There is currently no estimate as to when the line will reopen. However, trains are expected to be disrupted until approximately 5:30pm.”
Police and fire crews are currently attending the scene.