Nancy Gamerman, a Metro-North spokeswoman, said the fatality occurred when an unauthorized person was on the tracks at the station at 1:28 p.m.
Gamerman said it was too soon to say whether the person jumped on the tracks or was walking on them as the train approached.
She said more details -- including the person's ID -- would not be available for 24 hours.
Harrison Fire Department volunteers assisted at the scene.
Power was shut down on one of the tracks while the body was removed by firefighters.
The fire department requested a shutdown in both directions.
Metro-North announced that customers should anticipate up to 20-minute delays as a result of the police activity and to listen for announcements at local stations.
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