A decomposing body was discovered outside a Queens apartment building Sunday afternoon after residents whiffed an unbearable stench, according to police.

The body of an unidentified adult was discovered by cops at around 12:55 p.m. near scaffolding outside 92-40 Queens Boulevard in Rego Park, cops said.

The body was too badly decomposed to determine the person’s sex or identity — and whether foul play could be a factor in their death, the NYPD said.

The Office of Chief Medical Examiner will determine the cause of death, police said.

One longtime resident of the six-story building told The Post he initially believed the offensive smell — which had been lingering for some time — was dead rodents.

“That’s what I think [it was],” Jerry Bourder said. “Mice or rats or something like that.”