Lake Macquarie Police are investigating an armed robbery on a chemist outlet at Charlestown overnight.

Police say a man entered the Chemist Warehouse store on the Pacific Highway at about 9.30pm on Monday and left with boxes of perfume without paying.

An employee followed the man out the door and confronted him in the street but he allegedly turned around and threatened the worker with a knife.

The employee backed away and the man walked off.

He’s described as being Caucasian in his 20’s with a slim build and was wearing a black hooded jumper and cap.