Police had earlier said the robber, wearing red shorts, a black "hoodie" and a black and white bandana, fled from the bank to nearby Douglas McLean Ave.
Detective Sergeant Heath Jones said the robber was seen leaving the area with another person, but while the robber's clothing was discarded in an unoccupied Onekawa house, police had not found the suspect during the day, despite searches of properties in several suburbs.
A 22-year-old man alleged to have also been involved was arrested during the day, but no weapon had been found.
A witness told Hawke's Bay Today the robber spent several minutes in a nearby doorway and later on a seat watching for the opportunity to make his move, before entering the bank.
She said he had a knapsack which he had put on the ground and was fidgeting with a black and white bandana around his neck.
"He was fiddling with the knot at the back - he'd check it then pull it up on to his face - and kept playing with it," the woman said. "I thought it was strange - something didn't seem right." The man's plans seemed obvious to some in the shopping centre at the time, one man going into a nearby shop and telling staff: "I think that guy's just robbed the bank."
The witness left the shop and used his cellphone to call police, as the robber walked casually out of the post shop and up around the corner into Douglas McLean Ave and then into Bedford Rd.
A police spokesperson said the robber had walked in and approached a staff member while holding a firearm. He allegedly demanded money and the female staffer handed over what police described as "some cash".
"While no one was harmed staff were very shaken by the incident."
Teams of police swarmed into the immediate area and were told by witnesses that shortly after the robbery the man was seen cycling along Douglas McLean Ave with a second person, also on a bike.
Houses in nearby Bedford Rd became the initial focus of police dog teams and Armed Offenders Squad officers before the search switched to areas of Onekawa and Maraenui.
Clothes believed to have been those worn by the robber were found dumped in an empty house.
Teams of police went through a block of vacant houses off Roberts Tce in Onekawa while patrols set up a wide cordon by stationing cars at the intersections of Harold Holt Ave and Morris Spence Ave where they join Wycliffe St.