Police said the robbery happened about 6:05 p.m., when two men rushed into the store at 4326 N. Broad St. The first man, armed with an AR-15 style assault rifle, then forced employees to empty the cash registers.
The second man stood by the door as lookout.
The men took an undetermined amount of money, police said.
Hannibal said the store had dealt with thefts but nothing like Wednesday's robbery.
Several customers were in the store at the time and fled to the back, said Hannibal, who was working when the robbery occurred.
"Thank God none of them got robbed," he said.
Hannibal said employees were "dealing fine" after the incident.
Police described the man carrying the assault rifle as a black man in his late teens or early 20s, with a medium build, wearing a black neoprene ski mask, a black Nike hooded sweatshirt, black pants, an Armani Exchange belt, and dark sneakers.
The lookout was also in his late teens or early 20s, police said. His face was covered with an animal-print mask, and he was wearing an Adidas gray hooded sweatshirt, dark pants, and gray sneakers with bright-red laces.
Police have posted surveillance footage of the incident at http://blog.phillypolice.com and are asking anyone with information to call Northwest Detectives at 215-686-3353 or 215-686-3354.