A United Nations delegation visiting New Zealand prisons is warning that the high number of Maori in prison is a breach of international law.
More than half of New Zealand's prison population is Maori, although they make up just 15 percent of the population.
The delegation, which reports to the United Nations Human Rights Council, says any bias against Maori leading to their incarceration more than other New Zealanders constitutes arbitrary detention and is illegal under international law.
Speaking after a two-week tour, chairperson Mads Andernas said 50 percent of the male and 65 percent of the female prison population are Maori. Fifty-four percent of young people in Youth Court and 71 percent of child offenders in the Family Court are also Maori.
Mr Andernas said the New Zealand Government needs to investigate whether there is bias in the criminal justice system.
"There's every reason to go in and analyse closely in the criminal justice system the extent to which there is a systematic bias looking at certain socio-economic factors in a way one does when one is reviewing, for instance, parole."
Mr Andernas says sentencing and police arrest methods should also be part of the investigation.