A stranger stabbed a 41-year-old man to death in broad-daylight during a fight over a seat on an MTA shuttle bus, cops and sources said. 

Alvin Francis was on a shuttle bus traveling the J train route near Crescent and Etna Streets in Cypress Hills, Brooklyn, around 2 p.m. on Sunday when an argument broke out between him and another passenger wearing a backpack over seating arrangements, according to police and sources.

The enraged rider then knifed Francis in the stomach, police and sources said. 

The victim was rushed to Brookdale University Hospital Medical Center, where he succumbed to his injuries, cops said.

He lived several miles from where he was stabbed, in Jamaica, Queens, authorities said. 

The unhinged attacker — who was still at large Monday — was last seen wearing a gray sweat suit, police said.