The cash van, with four persons in it, had reached an State Bank of India ATM to fill cash in it, the police said.
The men were waiting for an opportunity to strike and as soon as the guard, Manoj, alighted, they shot at him and threatened the others at gunpoint and decamped with the bag containing cash, they added.
Manoj was rushed to a hospital where he is undergoing treatment.
The accused were wearing helmets so the victims could not see there faces.
Teams have been formed to trace the accused.