Whangarei Senior Sergeant Steve Dickson said police were investigating and the incident was being taken very seriously.
A resident of Guy Road, who asked not to be named, said police had been to his house looking for gunshot holes.
Michael Hunter, northern district secretary of the Postal Workers Union of Aotearoa, said it was disturbing to hear of a postie injured in such a way at work and there would likely be an inquiry into the incident.
"It is a rare event to be under siege by people shooting at posties with non-lethal weapons," Mr Hunter said.
"Most injuries happen when bikes slip on roads or are reversed into by cars."