A 45-year-old man was stabbed in the back during a Wednesday morning rush-hour clash inside the buzzing Union Square subway station, cops said. 

The victim was making his way toward the L train platform at the 14th Street-Union Square hub around 10 a.m. when the menace knifed him in the back during a dispute, authorities said.

He was taken to Bellevue Hospital, where he was listed in stable condition, police said. 

The male attacker fled the scene and was still on the loose Wednesday evening.

Entrance to the Union Square subway stationThe victim, 45, was stabbed twice in the back on the L train platform at 14th Street-Union Square, police said. LightRocket via Getty Images

It was not immediately clear whether the two men knew each other, or what sparked the violent dust-up. 

In an unrelated burst of violence a day earlier, a 15-year-old boy was stabbed repeatedly and left seriously hurt after a fight broke out on board a Bronx bus, cops and sources said.

The teen was knifed multiple times during a clash with two apparent strangers at Bartow and Wickham avenues in Baychester around 2:40 p.m., police and sources said.

Ambulance seen leaving Union Square.
NYPD investigation of earlier stabbing. One unidentified reportedly was stabbed in back and in not likely condition. Heard also on radio, perp fled onto a Brooklyn bound L train. Occurred on platform at rear end of mhtn bound L train. The stabbing stemmed from a dispute between the two men, authorities said. Robert Miller

It was unclear whether the boy was stabbed on board the bus or if he was attacked after getting off. 

He was taken to Jacobi Medical Center, where he was listed in critical but stable condition, police said. 

No arrests had been made by Wednesday.