A gunman fired a single shot on a Bronx MTA bus during a scuffle with a man whose teen nephew he had been harassing, cops said Thursday. 

The suspect approached an 18-year-old male passenger on the BX39 bus around 4:30 p.m. Wednesday and started asking him, “Where are you from?” and “Where do you live?” police said. 

Then he allegedly flashed a gun he had in his coat pocket, footage shows. 

Fearful for his safety, the teen contacted his uncle to pick him up at a nearby stop, cops said. 

When the bus stopped at White Plains Road and Van Nest Avenue, the teen’s uncle held the rear door of the bus open and told his nephew to come with him, authorities said. 

But the suspect confronted the uncle, sparking a physical fight, cops said. 

The gun went off during the struggle, striking the ceiling of the bus, police said. No one was hurt. 

The suspect then ran off the bus, heading north on White Plains Road. 

Cops say the suspect appears to be in his 20s and around 6 feet tall, weighing 165 pounds, with long, black hair. He was last seen wearing a green bubble jacket, a green hoodie and black and red track pants.