Dozens of shoppers inside the Northgate Shopping Centre ducked for cover when a gunman opened fire on Friday, Randburg police said.

Inspector Kym Cloete said the robber had confronted a security guard at around 9.20am as he was leaving Checkers after collecting a cash box. "The security guard attempted to pull out his weapon but it got jammed, and the suspect then fired a shot.

"Shoppers ran for cover," she said.

The gunman then grabbed the money box, ran outside and was seen getting into a car with other occupants.

Cloete said no injuries had been reported and no arrests had been made.

"Only one shot was fired and it was inside the shopping centre."