The suspect walked into the store at 115-01 Farmers Blvd. at about 9:50 a.m., showed a firearm and demanded money, according to the cops.
The cashier forked over an undetermined amount of cash, and the suspect then hit him in the head with the gun.
The suspect was described as about 30-years-old with dark eyes, short black hair and a dark complexion, police said.
He was last seen wearing a dark brown zip-up hooded sweatshirt, camouflage army pants and a ring on his left hand.
The cashier's condition was not available and the FDNY said it did not take anyone to the hospital from that location.
Anyone with information about the robbery or the identity of the suspect is asked to call Crime Stoppers at 800-577-TIPS (8477).