Boksburg North SAPS spokesperson Lieut Juanita Coetzer said the robber pointed a firearm at the guard and told him not to resist.
“The suspect then phoned his accomplices who were outside. They took cellphones from the store.”
There are reports that the men also stole jewellery and an undisclosed amount of money from the tills but Coetzer could not confirm this.
The men drove away in a white Toyota Tazz and a Silver Golf 5.
Coetzer said no shots were fired and there were no injuries reported.
Police are investigating.