Officials say the dispute happened at around 8:55 a.m. on the southbound 6 train platform.
The 41-year-old victim says he was arguing about space with another commuter. The other person then pulled out a sharp object and slashed the man in his face, authorities said.
The man was taken to NYU Langone Medical Center. Officials say the suspect ran away.
Police initially checked number 6 trains south of the station, but soon realized the suspect never actually boarded a train.
The suspect was described as a man in his 60s, with grey hair and a medium build, wearing a white shirt with black pants.
Service ran express from Grand Central-42 St to Brooklyn Bridge-City Hall for a short period of time, but has since gone back to normal.
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