An argument between two groups of teenagers after the train doors opened at the Mount Eden Avenue station in the Bronx turned deadly, police say, at around 4.30pm.
A 34-year-old man was killed, police said, while a 14-year-old girl, 15-year-old boy and three adults, ages 28, 29 and 71 were injured.
Some of the victims were believed to have been involved in the dispute and others were bystanders waiting for the train, with officers describing four of those injured as seriously wounded.
“We don't believe this was a random shooting. We do not believe that this was an individual indiscriminately firing into a train or a train station," NYPD's chief of transit, Michael Kemper, said.
A hunt was on for at least one shooter, who fled the scene. Police didn't rule out the possibility that more than one person fired shots.
Tarik Sheppard, the NYPD's deputy commissioner of public information, said: "To the shooter - you are now the NYPD's most wanted and you have the greatest detectives in the world looking for you. We suggest you turn yourself in."
The gunfire sent passengers rushing off the train while people on the platform scrambled for safety.
“The train was coming and there were two kids yelling," witness Efrain Feliciano, 61, told the Daily News. "There were at least six shots."
"I saw sparkles as the bullets hit the wall," he added "A woman was holding a child screaming."
Video from television news helicopters showed the train stopped at the station and orange evidence cones on the platform, which is three stops north of Yankee Stadium.
"It was total pandemonium," Luis Rodriguez, 34, told The New York Post. "It makes you scared to ride the train."
Speaking after Monday’s shooting, New York Mayor Eric Adams acknowledged that more needs to be done to make people safe when riding the subway.
He told 1010 Wins radio: "Not only people must be actually safe, but what we have done in lowering crime, they must feel safe and something like this can send shockwaves throughout our entire system.”
Around 3.8 million trips are taken on the New York's subway system on an average weekday, with around 570 felony assaults reported in all of 2023.
Shootings on the subway are even more uncommon.
In 2022, when a man with a handgun injured 10 people on a train passing through Brooklyn, it was the first mass shooting attack on the subway system since 1984.