A police dog handler was assaulted during a routine stop of a vehicle on Bairds Road, Otahuhu, at about 3.50am on Saturday 28 May, 2016.
As he spoke to the driver, two men got out of the car and assaulted the officer. He was knocked unconscious before a passing truck driver scared off his attackers, who fled in a green Toyota Alteeza.
A passing ambulance treated the officer and took him to hospital, where his condition is described as moderate.
His attackers are described as being of average height and build. One of them was wearing a black t-shirt with white writing on it.
Anyone who may have seen the car or have any information about the offenders is asked to contact Crimestoppers on 0800 555 111.