The officer was identified as a member of the Umlazi tactical response team, while the wounded man was taken to hospital under police guard, Captain Thulani Zwane said.
The robbery took place on Friday, with three other robbers fleeing the scene with an undisclosed amount of money in a Toyota Corolla and an Isuzu bakkie.
An inquest docket was opened, with a case of business robbery and attempted murder to be investigated, Zwane said.
The officer's firearm was found on the scene. It would be sent for ballistic tests to see if it was in used in any other crimes in the province.
Provincial police commissioner Lieutenant-General Mmamonnye Ngobeni was concerned by the involvement of police officers in criminal activities.
"We will work hard to get rid of corrupt police officers from the services," Ngobeni said.
"Our loyal members will work around the clock to trace those suspects who fled the scene with stolen cash."