Nearly half of sex offenders with the highest risk of reoffending broke special supervision orders when released back into the community, according to the latest figures.
And a steady rise in the number of convicted sex offenders being placed under what are known as extended supervision orders has alarmed advocates.
The figures provided to the Herald by Community Probation Services (CPS) show the number of people on the orders has risen each year since 2008, with nearly 200 registered at the end of the 2011 reporting year.
The orders, which can be imposed for up to a decade after the offender has been released, are generally enforced on those who have been assessed as having the highest risk of reoffending sexually against children, those with offences relating to child pornography, or those who have committed sexual offences against victims with significant impairments.
The orders can restrict where they live and work, their use of mobile phones and the internet, and force them to attend treatment or counselling. Breaking them carries a maximum penalty of two years in prison.
Sensible Sentencing Trust spokesman Garth McVicar described the CPS figures as "alarming".
"It also indicates how seriously we have got to take this problem. We deal with a lot of victims of these crimes and it horrifies me that many of these offenders are still out there in the community."
Former Act MP Deborah Coddington, who published a book listing convicted paedophiles and sex offenders since 1996, said New Zealand had a "long way to go" in dealing with sex offenders.
She agreed with a hard-line proposal unveiled in November by the National Party to indefinitely hold the worst prisoners, across all offences, who were at imminent risk of re-offending, even if it crossed rights enshrined in the Bill of Rights Act.
"With these types of offenders, you have to err on the side of caution, because in the main these offenders are very manipulative and will go to great lengths to groom or get access to victims," she said.
"I'm not in favour of locking people up and throwing away the key - but with this very small number of irredeemable offenders, we just have to bite the bullet."
Rape Prevention Education executive director Dr Kim McGregor believed it was unsafe to release high-risk potential reoffenders into the community.
"But most importantly, it's not just about containing people - it's ensuring they are having treatment."
She said a recent report found that sex offenders who completed treatment had a "very small" recidivism rate of around 5 per cent.
The CPS could not provide information on the nature of the breaches and the specific charges that followed.
But CPS acting general manager Astrid Kalders said the breaches could have been for violating "the most simple of conditions", such as using cellphones when ordered not to. She said the number of recorded breaches showed the orders were being maintained and that offenders who failed to comply were being held to account.
In the past year, CPS had made "significant improvements" to the way offenders were managed.
"Probation practices have been redesigned, from being highly prescriptive and procedure-based to being clear about activities that are mandatory while supporting professional judgment and decisions on offender management, with a focus on medium and high risk offenders."
There was a general drop in reconviction rates among all sex offenders between 2008 and 2010, which likely reflected changes to management practices, she said.
Before approving suitable addresses for sex offenders being released back into the community, CPS undertook checks, including proximity to schools, parks, kindergartens, libraries, thoroughfares, and other areas frequented by children. Communities were notified of offenders living among them on a case-by-case basis in line with the Privacy Act.