Surveillance video from inside a Bronx building shows three young men beating and robbing a food delivery worker.

The ambush happened inside a building on Walton Avenue near Marcy Place in West Concourse around 2 p.m. Aug. 24, police said.

The thugs are seen waiting at the bottom of a flight of stairs for the victim to come down before one of them punches him in the face, knocking him backward onto the stairwell.

Two of the suspects then dig through his pockets and steal around $150 before the trio flees.

The worker refused medical attention at the scene.

The suspects are all believed to be in their late teens or early 20s, police said.