New York police said a 48-year-old man was shot and killed on Sunday on a subway train in Lower Manhattan, and investigators believe the attack was unprovoked.

The unidentified gunman fled when the train pulled into the next station, and remained at large on Sunday night, Kenneth Corey, New York City Police Department (NYPD)'s chief of department, said at a news briefing.

"Preliminary investigation reveals the suspect was walking back and forth in the same train car and, without provocation, pulled out a gun and fired it at the victim at close range as the train was crossing the Manhattan Bridge," Corey said.

The gunman, described only as a heavy-set, "dark-skinned" man with a beard who was wearing a hooded sweatshirt, gray sweat pants and white sneakers, fled when the train pulled into the Canal Street station.

The suspect and the victim were not acquainted and had not interacted prior to the gunfire, police said. The victim, who was not identified by police, was pronounced dead at Bellevue Hospital shortly after the 11:40 a.m. shooting.

New York Governor Kathy Hochul condemned the "horrific" crime on Sunday, vowing that the gunman would be caught.

New York City has seen a sharp rise in violence and a series of random attacks on subway riders.

The transit violence has included passengers pushed onto the tracks from platforms, including a Manhattan woman whose murder was seen as part of a surge in hate crimes against Asian Americans.

On April 12, a gunman set off smoke bombs and opened fire in a subway car, wounding more than 20 people. A suspect was taken into custody the following day.

"It's pretty harrowing stuff," rider Arsenault Rivera told the New York Times. "If I'd gotten on at a different point, I would have been right there."

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(With input from agencies)