A Manhattan man died of an apparent overdose after an ambulance failed to show up at his building for more than an hour, forcing frustrated cops to finally rush him to the hospital, to no avail, police and law-enforcement sources said. 

Adam Benhammou, 22, of East Harlem was showing signs of an overdose at his building on East 116th Street near Lexington Avenue at 5:13 p.m. Saturday when a 911 call was made asking for first responders’ help, according to authorities and sources. 

When NYPD officers arrived at the scene at 5:40 p.m., they found Benhammou “having trouble breathing and acting erratic,” sources said. 

Four minutes later, the cops radioed for an ambulance to come in “a rush,” according to the sources.

By 6:05 p.m., cops again requested for an ambulance to come quickly and asked for its estimated time of arrival, but none was given, the sources said. 

When the ambulance had not arrived by 6:25 p.m., the officers loaded Benhammou in the back of their police cruiser and brought him to Harlem Hospital, arriving 4 minutes later, according to sources. 

But Benhammou ultimately could not be saved and was pronounced dead by hospital staff at 6:56 p.m., sources said. 

The FDNY, which oversees 911 ambulances, told The Post on Tuesday that the incident is “currently under investigation.” 

The death also is being probed by the NYPD’s Force Investigation Division, which probes all deaths in police custody. 

Benhammou’s official cause of death will be determined by the city medical examiner’s office.

Santiago Ortiz, 79, who lived in Benhammou’s building with his wife for 46 years, said the delayed ambulance didn’t “help at all.

“When there’s an incident [in this neighborhood], the ambulance comes right away,” Ortiz said. “I don’t know what happened this time.”

When told of Benhammou’s death, Ortiz exclaimed, “Oh, my God!

“That sucks,” he said. “It shouldn’t have happened, and we have hospitals close by.”