An investigation has been launched after a video showed Oranga Tamariki staff violently restraining a vulnerable child, actions slammed as "totally unacceptable" by Children's Minister Kelvin Davis.

Davis also praised the staff-member-turned-whistleblower who provided the footage to media and spoke out about what they felt were illegal constraints constituting assault.

Oranga Tamariki chief executive Sir Wira Gardiner said he had watched the video also and was "deeply concerned are deeply concerned that excessive force looks to have been used against children and young people in our care".

"This is unacceptable behaviour and we will start an investigation today into the circumstances shown in the video," Gardiner said.

The video, published on Newsroom, shows a boy aged around 13 in one of the state child protection agency's Care and Protection Residences being tackled, held on the ground by three staff members, his face pushed into a wall and arms twisted behind his back.

Another boy of a similar age is shown in a video being placed into a headlock and also thrown to the ground.

The whistleblower told Newsroom such residences were for the country's most vulnerable young people, who hadn't committed a crime, were not being held as punishment and often came from years of violence and trauma with complex needs.

He said the restraints shown were "unprofessional, inappropriate and abusive" and if conducted by police they would be charged with assault.

Davis said he had seen the video and called the practices "totally unacceptable".

He said he had asked Oranga Tamariki to review the incidents and each of the care and protection residences to ensure the practices were not widespread.

"I've asked Oranga Tamariki officials and the independent advisory board to be on site and get to the bottom of things."

He declined to label the actions assault nor abuse, saying that was up to authorities including police to determine.

"Obviously it is not best practice, it won't help these kids whatsoever.

"It is totally unacceptable but others will be the judge if they are breaking law. That is the sort of behaviour we have got to address in any residence. We have to make sure no further harm and trauma is added to their lives.

"Anyone who thinks they have stepped outside of the law should make a complaint to police and it is up to police if they lay charges."

There are three such residences in the country - in Wellington, Christchurch and Dunedin - with roughly 100 children placed there each year. More than two thirds are Māori.

They differ from Youth Justice facilities, and children are not there for criminal offending.

Davis said ratio of social workers in such facilities had changed in recent years and he had asked for more information and to make sure the right people with the right skills were working in these residences.

"I think their needs are greater, and we need people with greater skills to deal with their behaviour

"It is a difficult job but there is no excuse for what we have seen in the videos."

Davis said he supported actions by the whistleblower to "raise issues around bad practices".

"Oranga Tamariki needs to ensure it has a robust system so reports of bad practice are acted upon."

Prime Minister Jacinda Ardern said she had been briefed on the video but not had a chance to see it.

"I understand the Minister for Children has asked for an explanation.

"Our priority in these environments where we have the responsibility for the care and protection of children is to make sure everybody is behaving to the standard we expect.

"We have a responsibility as the state when children are in our care even in the most difficult circumstances we are applying standards."

In response to the revelations Gardiner said their first priority was to support the young people shown in the footage and their whānau.

"We will be talking with all our tamariki and rangatahi currently in our Care and Protection residences.

"We also encourage any young people or staff who are concerned about experiences that they may have with [management of actual or potential aggression] (MAPA) holds to contact [email protected]."

There was CCTV in all residences to support keeping young people and staff safe, he said.

"There are well established systems and processes in place to review events like this when escalated to us.

"Any restraint or use of force is expected to be reported and is investigated.

"Referral to the police and subsequent employment authority is taken whenever the actions were incorrect, unnecessary and, or unlawful."

All Oranga Tamariki staff in care and protection residences were trained in the correct MAPA hold technique, he said.

"We will be reminding staff of this and working alongside them to ensure that they're equipped and confident to use MAPA safely and correctly.

"All young people in our Care and Protection residences are particularly vulnerable and have suffered trauma. We must do better to ensure that they feel safe and supported while in our care."

Children's Commissioner Andrew Becroft said his office had asked Oranga Tamariki to call in police over the allegations by activating the Child Protection Protocol.

"On the face of it, the videos show violent attacks on children, by those who are supposed to be caring for them. These children are living in care and protection 'residences' usually because they've experienced traumatic upbringings and there is often nowhere else for them to go. These are not youth justice facilities and children are not there for criminal offending.

"The behaviour on the video appears to be neither care nor protection; and it should shock every New Zealander to the core. There is a clear need for Oranga Tamariki to activate the CPP and trigger an investigation of possible abuse."

Becroft said the treatment highlighted why such residences needed to be closed, and how crucial it was the new Independent Children's Monitor – soon to be hosted by ERO - was "truly independent of Government and can stand up for children in the state's care".

Oranga Tamariki told Newsroom 223 holds had been applied in residences in 2019 and 170 in 2020.

It said a total of 12 restraint-related injuries had occurred in Care and Protection Residences over the past two years, but noted these figures could include "minor bumps and scrapes".