A woman shoved an unsuspecting traveller off a New York City subway platform into the path of an approaching train on Monday afternoon, killing the victim instantly as bystanders watched in horror.

The victim, a 46-year-old woman, was pushed onto the tracks as a southbound No. 1 train pulled into the Times Square station around 1 pm, and she was pronounced dead on the scene shortly afterwards. Witnesses immediately alerted police officers, who apprehended the suspect in the station.

Neither the victim nor the suspect was immediately identified by authorities.

"What happened here today is tragic," Joseph Fox, chief of transit for the New York City Police Department, said at the midtown Manhattan subway station, one of city's largest and busiest.