A city correction officer was busted on murder charges for allegedly gunning down his uncle on the Upper West Side on New Year’s Day, police said Thursday.

Cops say the off-duty officer, Cardell Gadsden, 30, and his 37-year-old uncle Steven Gadsden were inside a car with another man on Manhattan Avenue and West 107th Street at around 9:45 p.m. Wednesday when the relatives got into a spat.

The argument between the uncle and nephew escalated and spilled out onto the sidewalk where Cardell allegedly blasted Steven in the chest, killing him, before walking away, police said.

Medics rushed the victim, who lived on West 114th Street, to Mount Sinai St. Luke’s Hospital where he was pronounced dead.

Shortly after the fatal incident, Cardell returned to the crime scene while it was still active and surrendered to police, according to cops. He was charged with murder and criminal use of a firearm.

It was not immediately clear what the relatives had been arguing about.

The other man, 40, inside the car — who was sitting in the driver’s seat and who a police source says was a friend of the relatives — remained at the scene and was not arrested, cops said.

Department of Correction Deputy Commissioner Peter Thorne said in a statement Thursday that Cardell has been suspended without pay pending the results of an NYPD investigation.

“We are deeply troubled by these allegations and our condolences go out to the victim’s family,” Thorne said.

Cardell, who has worked for the DOC since August 2015, raked in a total pay of $73,168 for the year of 2019, according to data posted by SeeThroughNY.

Meanwhile, neighbors of Steven, who say that he had been staying with his mother at an apartment on West 114th Street, were stunned by the incident.

“He was a great guy. Very friendly,” one neighbor said of Steven. “Every time I see him he had a smile. Right now I’m trying to deal with this. I’m still in shock. I’m still in disbelief. He was such a good guy. Everybody right now is still in shock.”

Steven’s mother, Lydia Gadsden, sobbed when reached by phone Thursday by The Post.

“I can’t talk right now. I don’t know anything,” she said through tears. “We don’t know what happened. There’s nothing I can tell you.”

Another neighbor suggested that there had been bad blood between Steven and Cardell.

“They weren’t supposed to be around each other. But they was family. It’s messed up what happened,” the neighbor said, adding that “it’s crazy.”

“[Cardell] messed up his whole f–king life.”

Additional reporting by Tina Moore