The murder and manslaughter of about 100 people a year makes New Zealand one of the most violent countries in the developed world, according to a new independent report.

New Zealand has been given a "D" rating on a report card prepared by the New Zealand Institute, because of its high rates of violent deaths and child abuse.

This weekend, the United Nations Human Rights Committee expressed concern at New Zealand's high rates of child abuse, and recommended the Government encourage reporting of suspected abuse, and ensure the perpetrators are brought to justice.

According to the New Zealand Institute, only Mexico, Finland, Hungary and the gun-toting US have higher "assault mortality" rates in the 30-member OECD, the Organisation for Economic Cooperation and Development.

Australia's violent killing rate is half that of New Zealand's, while table leaders Japan and Britain have only a quarter the per capita rate.

The institute's study has been two years in the making, and uses a series of measures to make its findings.

The independent thinktank concluded that assault mortality rates were the "tip of the iceberg of violence in a country".

Many people are affected. For every violent death, there are another 1000 violent crimes reported, the Institute reports.

And family violence accounts for about one-third of assault mortalities - and costs the country $1.2 billion a year in police investigations, criminal trials, jailing the offenders and helping the victims.

Violence against children accounts for around one third of the deaths - and is rising.

The institute is an independent think-tank founded in 2004 to investigate long-term improvement of the country's social, economic and environmental performance.

The institute's director Rick Boven labels the D grade "a failure for society as a whole".

He expects the grade to be controversial but stands by the analysis: rather than damning the country, he said, the assessment should be used to invigorate debate on how to improve policy.

"There's not enough being done to make a difference".

Police and Corrections Minister Judith Collins attributed the high violent death rate to those "beating up their families" and those - usually relatives - who turned a blind eye.

"The people who hit and kill and starve children are who should be blamed," she said.

A string of policies to combat violence, from teenage boot camps to on-the-spot police protection orders, were examples of more proactive policing, she said.

But government agencies were "often the ambulance at the bottom of the cliff".

She said New Zealand had a culture of making excuses and blaming government departments, rather than holding violent offenders responsible for their actions.

Criminologist Greg Newbold, like Collins, was not surprised by the D rating.

He said Kiwis had to recognise they had a problem, and blamed political correctness for a government failure to deal with "shameful" Maori assault and child abuse statistics.

He said many children were brought up witnessing violent talk and behaviour and then copying it.

The Associate Social Development Minister, Tariana Turia, said "we clearly need to do more", and the $2 million Family Violence Whanau Ora funding should be a step in the right direction.

"Just as agencies need to be vigilant in identifying situations of risk and following up, so too should all of us take responsibility in our own homes," she said.

Sensible Sentencing Trust spokesman Garth McVicar blames lawmakers for more criminals "evolving".

He said youth ultimately needed "real consequences" and "earlier consequences" for bad behaviour. Then they might have a hope of being turned around, McVicar said.

On Wednesday, the New Zealand Institute is to publish a full report card on how this country ranks against others in the OECD on various measures, including our health, education and life expectancy.