The United Nations Committee Against Torture says it is "deeply concerned" about New Zealand police adopting the Taser stun gun, as it releases a growing list of worries about this country's justice system.

The committee has released its fifth report on New Zealand, which covers the period 2003 to 2007.

While it approved some moves the repeal of Section 59 of the Crimes Act, which removed the defence of reasonable force for parents who physically punish their children, there was a longer list of concerns, including worries about the use of Tasers by police.

The severe pain they caused could be seen as a form of torture and could even kill someone.

During the trial period the Taser was mainly used on Maori and youth, which was concerning, the committee said.

It was also concerned about the impartiality of the Independent Police Conduct Authority, which included current and former police officers.

That could hamper investigations into allegations of acts of torture and ill-treatment by the police, the committee said.

Green Party human rights spokesperson Keith Locke said the Government should take note of concerns raised about the use of the Taser.

"New Zealand politicians should listen when a reputable UN committee says this 50,000-volt stun gun inflicts 'a form of torture' on its targets," Mr Locke said.

Police had a "pretty easy ride" in introducing the Taser, with the authority ignoring concerns many had, Mr Locke said.

"Prime Minister John Key needs to re-think his recent statements giving the green light to all front-line police having access to Tasers."

Human rights lawyer Tony Ellis said the UN committee's 2004 report contained eight recommendations, but the latest contained 18.

There were clear defects and given the large number of recommendations the Government needed to give serious consideration to address those, he said.

Among the other concerns of the committee were:

- a disproportionately high number of Maori and Pacific Islanders in prison, and in particular the number of women represented by those groups -- 60 per cent of the female prison population.

- Asylum seekers could be deported without detailed reason or revealing classified information.

- The low age of criminal responsibility.

- Juvenile offenders were not systematically separated from adult offenders.

- Insufficient numbers of prisons to cope with forecast growth, and also inadequate mental health facilities.

- Allegations of cruel, inhuman and degrading treatment against children and patients in psychiatric hospitals were not being investigated and perpetrators not prosecuted.

- New Zealand's Bill of Rights had no higher status than ordinary domestic legislation.