A 5-year-old boy wearing nothing but diaper fell from a fourth-floor window of a Bronx apartment building onto the sidewalk on Sunday evening, August 9, police said. 

The boy fell from the building on Buchanan Place near Davidson Avenue in University Heights around 5:30 p.m., police said. 

He tumbled from the fourth-floor window and had “injuries indicative of falling from an elevated position,” according to cops and law enforcement sources. 

Video from the scene shows the child kneeling motionless on the sidewalk, with his head on the ground and arms outstretched. 

In a video of the aftermath posted on social media, people surrounded the boy and expressed disbelief. 

“Wow, a boy just fell out the window!” one onlooker said. 

“Where is the f**king parents, man?” another could be heard shouting. 

Two cops turned the child on his side as another onlooker said, “God bless him,” the clip shows. 

Witness Tone Rodriguez told WCBS he and other pedestrians were standing outside when they heard a loud thud. 

The boy had several scratches on his face, he added. 

“His face was all swollen on this side. He was like, you can tell he got hit bad. We were trying to figure out where he came from,” Rodriguez said. 

The boy was taken to NewYork Presbyterian Hospital, where he was listed in critical but stable condition. 

No arrests have been made and no criminality was immediately suspected, cops said.