A knife-wielding crook dressed as a construction worker was caught on video beating a worker as he robbed $3,000 from the pharmacy at a Bronx Walgreens, police said.

The thief walked into a restricted area of the store at East 161st Street and River Avenue and knocked on the door to the back office around 8:30 p.m. Monday, cops said Thursday morning.

When a 21-year-old male employee opened the door, the robber pulled out a knife from his black and blue duffel bag and tackled the worker to the floor. The suspect then ransacked the office, cleaning out the safe and register drawer.

The crook then ran out of the drugstore through a back door and fled southbound on Morris Avenue.

The heist was captured on camera, with the thief wearing a white helmet, a neon green and orange work vest, a black hooded sweater, blue jeans and tan boots.

Police are looking for the individual, described as 20 to 25 years old.