Oranga Tamariki says the video that has been circulating online of two teenage boys attacking one another at its youth justice unit was filmed by a staff member.
The incident took place on 16 June at its Auckland facility, Korowai Manaaki - the same place where five youths were on the roof at the weekend causing significant damage.
Oranga Tamariki deputy chief executive Tusha Penny told Morning Report the staff member's actions were "totally unacceptable and there are no excuses for it".
Four staff members have now been removed from the facilities and Penny said this was the only incident she was aware of that was videoed by a staff member.
"In saying that, I have been involved in the residences for two weeks," she said.
A site manager came across the video online five days later and forwarded it to the national office and then to police. Penny said there is CCTV around the complex but it did not pick up the fight.
Penny said Oranga Tamariki was dealing with "really challenging and complex teenagers" who have "committed very serious crimes in the community".
"We have staff onsite 24/7 working and looking after them," she said.
There are areas where youths have shared accommodation and also "secure" areas where Oranga Tamariki staff can put young people "if they have committed offences or if their behaviour meets the threshold, for a short period of time".
But Penny said on the whole, young people have the freedom to walk around and do things as they should.
She said the training of the staff there was under review. Currently, they undergo training for "a couple of weeks" and are police vetted.
"We have to make sure that our staff are appropriately vetted and appropriately trained," Penny said.
"Yesterday I was sitting with...a social worker who has been [working for] 20 years and she was crying about this. She said, 'this is not who we are'. It's not who Oranga Tamariki is and this behaviour in these residences is going to stop."
Penny said she could not confirm whether there was organised fighting in Oranga Tamariki facilities.
"Because of the actions we've taken...to flush out everything, we're asking for our staffers...to come forward if they know anything."
Police have confirmed they are investigating a fight at an Oranga Tamariki facility last month.
A spokesperson said no charges have been laid and the enquiries were continuing.
Penny also spoke about the incident over the weekend, where initially eight young people forced their way onto the roof at the same facility.
She was not aware that was a protest.
Penny said police negotiators told her the motivation behind the disruption was a list of demands from the youths.
"Their demands...were things like, they didn't want to go into custody, they wanted to be kept together, that group, they wanted to call girlfriends, they wanted food, there was initially quite a long list."
The standoff was eventually resolved late on Sunday night and the group are in police custody.