A chainsaw has been used to damage two significant pieces of Maori art work on State Highway 36 at the entrance to Rotorua from Tauranga.
One of the pou has been felled and the other badly damaged.
The vandalism was first reported by an off-duty member of police.
The damage occurred sometime between 6pm on Thursday and 8am on Friday, with the police hoping witnesses can help to narrow down the time-frame.
A forensic examination has been carried out and iwi leaders have been informed.
Police say they will be stepping up overnight patrols in an effort to prevent further vandalism until those responsible are caught.