Spokesman for the police in the state, Mr. Ben Ugwuegbulam, said in Port Harcourt the robbery took place between 8am and 9am along the Isaac Boro Park flyover in the city.
He said no arrest had been made but that the police were investigating the matter.
According to him, the policeman was injured while responding to a distress call and tried to foil the operation together with some other policemen.
Ugwuegbulam however said the robbers got away with their loot but promised that the police would track them down.
He said the victims of the robbery were conveying an undisclosed sum of money in a commercial vehicle when they were attacked.
He explained that there was no country in the world that was crime-free, adding that the command was doing everything possible to protect lives and property in the state.
State Commissioner of Police, Mr. Muhammad Indabawa, on August 31, told a news conference that 13 policemern were killed by robbers between April and August this year.
Indabawa said the police had in return shot dead 36 armed robbers and kidnappers, and rescued 17 kidnap victims during the period.