A man was found fatally stabbed on a No. 4 train in Union Square early Saturday morning, police said.

According to authorities, a passenger traveling on the southbound train in Manhattan just before 4 a.m. noticed the man slumped over and alerted the conductor at the 14th Street station.

The 32-year-old victim, who was stabbed in the torso, was taken to Bellevue Hospital Center, where he was pronounced dead.

The circumstances of the stabbing are unclear, as there were no signs of a dispute on the train. It wasn’t clear whether he was stabbed on the train, or before he got on board.