Teenagers were unlawfully detained for weeks on end in the seclusion wing of a youth justice facility run by Child Youth and Family, according to its own senior staff.
Documents obtained by the Herald also reveal:
• staff used "inappropriate force" against young people.
• secure care was used as punishment.
• some young people were stripped and put in suicide gowns..
• a "significant number" of teens should not have been put in seclusion in the first place.
Children's Commissioner Judge Andrew Becroft told the Herald there had since been significant improvements at the facility - but the reported breaches were serious and unlawful.
"Secure care is not something used lightly...the regulations are non-negotiable, and while not a breach of primary legislation, still have the full force of the law behind them," said Becroft, who is a former Principal Youth Court Judge.
"Therefore, any breach of these regulations is illegal."
CYF had the legal right to detain the young people at Christchurch's Te Puna Wai o Tuhinapo - but when they were put in secure care their cases weren't reviewed daily, as required by law.
Senior CYF staff concluded the lack of daily reviews meant some young people were illegally detained - a view the agency now says is incorrect.
All youth justice residences have a secure care unit - a section where young people are placed as a last resort if they become a danger to themselves or others.
CYF says people held in the unit mix with other young people and staff and take part in rehabilitation programmes including schooling.
However, the Office of the Children's Commissioner, which has its watchdog role under the Crimes of Torture Act, still considers secure care as a form of segregation that can affect a detainee's mental and physical health.
Sign-off from a judge is needed if secure care detention is to exceed 72 hours.
The law also requires a daily review of each young person by the staff member in charge of the unit, to ensure they do not stay any longer than absolutely necessary.
Documents released to the Herald under the Official Information Act show that didn't happen in some cases.
Summary notes from an October 16, 2014 phone conference that included chief social worker Paul Nixon stated three young people had been in secure care since September without having their retention reviewed. "These are therefore illegal detentions," the note states.
Staff used non-approved methods of restraint and there are repeated references in records of young people "going to ground" while being restrained.
"Staff see themselves as needing to be seen to 'win' situations with young people," the phone conference note states, adding that secure care was incorrectly used as punishment for behaviour.
CYF were unable to confirm how long the young people referred to were in in secure care or if they were informed of the review failure, saying more time was needed to find records.
Since December 2012, 10 staff faced disciplinary action for excessive force, with the most recent in November 2015.
Chris Polaschek, CYF's general manager of youth justice support and who was on the conference call, said the detentions were mistakenly referred to as illegal, "but in fact relates to regulatory compliance".
"The concern is...reviews were sporadic, of low quality and/or not being appropriately recorded so that evidence existed that they were actually occurring."
CYF was working through records and if it was found that the regulations breach caused harm "appropriate action will be taken accordingly".
In June, then-Children's Commissioner Dr Russell Wills highlighted concerns about Te Puna Wai in an annual State of Care report, giving the residence a "detrimental elements" rating - although follow-ups led him to state the residence was "back on track".
The OCC has made a further visit since, and Becroft said he believed the facility was moving in the right direction and young people and staff are safe.
He will soon ask the Government for more money to enable inspections of residences every six months and not the 18, and to get beefed-up inspection powers.
"I want to get right to the bottom of exactly what is done, day-by-day...our office has taken it very seriously. But our senior staff desperately want to [inspect] more regularly. But we are unable with current funding to do that."
Social Development Minister Anne Tolley said as part of an overhaul of care for young people - which will see CYF replaced with a new Ministry for Vulnerable Children in April - the future of residences would be considered, including if "community-based options might be more appropriate, keeping safety in mind".
"The role of the Children's Commissioner is likely to change as a result of the overhaul of New Zealand's care and protection system and we'll be looking at funding when that becomes clearer."
Labour's justice spokeswoman Jacinda Ardern said she had spoken to a staff member who had recently left Te Puna Wai, and had been told severe issues remain and the risk there was "still extreme".
New Zealand First spokesman for Youth Affairs Darroch Ball said MPs needed to be given access to youth justice facilities, in the same way that they can currently had the right to visit and monitor adult prisons.
"MPs have the right to ensure anyone detained is safe, cared for and that the residences are adequate. This shouldn't be limited to prisoners who are 17 years and older."
- Additional reporting: Kirsty Johnston
Te Puna Wai youth justice residence
• Young people held in secure care without having detention reviewed as required by law.
• Staff used "inappropriate" force, and secure care was used as punishment.
• Children's Commissioner says remedial action appears to have put facility back on right track.