Police are warning a Maori independence group that it has no authority to enforce policing laws.
The group, Native Pirihimana (Native Police), has been patrolling Waikato in black vehicles marked with blue and red stripes and the group's signage.
Native Pirihimana says it wants to work alongside police and its duties include helping the public when called upon, and monitoring police activity.
The group says it should be entitled to establish an indigenous police force under the Treaty of Waitangi.
The group's commissioner, Rex Dennis-Ansley, hopes in the future it will be able to set up a policing unit modelled on an American Indian policing reserve scheme.
Mr Dennis-Ansley says members of Native Pirihimana are based throughout New Zealand.
However, Superintendent Wallace Haumaha says the group will be prosecuted if it is found to be interfering in the course of justice, and this could result in 12 months' imprisonment or a fine of up to $15,000, or both.
Mr Haumaha says police are considering setting up a campaign to raise public awareness that Native Pirihimana has no authority to enforce laws.
Meanwhile, Native Pirihimana, which is funded by donations, says it plans to lodge an application soon for police funding to help in its work.