It happened around 10:30 a.m. on the 4/5 train northbound platform.
Officials said 29-year-old victim was helped back onto the platform by fellow riders and suffered minor injuries.
She was rushed to a waiting ambulance and transported to Bellevue Hospital.
It was unclear what -- if anything -- prompted the incident, but it was described as a deliberate and apparently random act.
The unknown suspect fled the scene.
Police described him as a heavyset black man who was wearing a black jacket with a gray hoodie underneath, dark pants and dark shoes.
Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).
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