An off-duty security guard at a Manhattan shelter was shot Monday afternoon near Madison Square Park — and police believe the assailant opened fire over an ongoing clash, law enforcement sources said.

The victim, 49, was blasted in the torso just after 12:30 p.m. on Madison Avenue near East 28th Street in NoMad – steps from The Prince George, a shelter run by the organization Breaking Ground, where he works, cops and sources said.

The guard, who wasn’t working when he was shot, according to sources, was taken to Bellevue Hospital, where he was listed in stable condition.

The victim knew the shooter, and the pair had an ongoing dispute, the sources said.

The suspect apparently came back to the shelter and shot the guard, days after their feud began, according to the sources.

It was not immediately clear what, if any, connection the suspected shooter had to the shelter.

No arrests have been made, police said.

The violence came just hours after a 40-year-old man was shot dead outside a Brooklyn home, police said. 

The victim — who was not immediately identified — took bullets to the torso and right leg around 9:10 a.m. outside the residence on Wortman Avenue near Ashford Street in East New York, cops said.

He was taken to Brookdale University Hospital Medical Center, where he was pronounced dead.

He and the alleged gunman were seen together on surveillance footage just before the shooting, and it appeared the victim was targeted, sources said.

The motive remains under investigation and no arrests have been made, police said.