A woman was killed instantly after she was pushed in front of a New York subway train during the morning rush hour.
The victim was shoved onto the tracks by a woman as horrified commuters looked on.
The suspect was apprehended by police at Times Square station and taken into custody.
"What happened here today is tragic," Joseph Fox, chief of transit for the New York City Police Department, said.
The victim was standing on the platform when the suspect lunged at her, police said.
Witnesses said the victim and suspect were arguing before the incident, but it was not clear whether the two women knew each other.
Emergency services were working to remove the woman's body from the tracks before the evening rush hour.
Investigators were reviewing surveillance video and interviewing witnesses to determine a motive, said William Aubry, the police department's chief of Manhattan detectives.