A 49-year-old man was stabbed during an early-morning clash when he bumped into a stranger just outside the Port Authority subway station Friday, authorities said.

Guarionex Torres was knifed in the neck and groin during a fight with Jesus Ramirez, 28, at West 44th Street and Eighth Avenue in Hells Kitchen just before 1 a.m., according to cops. 

Video from the scene shows Torres riding up to Ramirez on a Citi Bike, according to police sources. The two exchange words before Ramirez stabs Torres, the sources said.

Cops say tensions flared when the two men bumped into each other. 

Torres was rushed to Bellevue Hospital, where he was pronounced dead. 

Ramirez was arrested on the scene and charged with murder and criminal possession of a weapon, police said.

He is claiming self-defense, according to police sources.

He has a single prior bust in 2011 as a 17-year-old, for trespassing, the sources said. 

Torres has more than 30 prior arrests, police sources said. 

Just two weeks ago, he was busted for swinging a hatchet at people near the Port Authority Bus Terminal, according to cops and police sources.

He was charged with menacing and criminal possession of a weapon, the sources said. 

A knife was recovered near the scene, cops said. 

Brass knuckles were also recovered, police sources said. 

Photos show a Citi Bike on the ground near the taped-off scene.