The 42-year-old received serious head injuries in the assault, which occurred on Kitchener St around 3.40am on Saturday, a police spokeswoman said.
Taranaki Daily News reports Police have reissued an appeal on Monday for witnesses to come forward.
The cause of his injuries was not yet known, the spokeswoman said.
The man was seen walking down the middle of Kitchener St, obstructing the flow of traffic, when a car stopped and "words were exchanged" between the victim and the occupants of the car.
