Oranga Tamariki is investigating whether a worker at a youth justice facility in Canterbury used force against a young person.
The incident is one of three at Te Puna Wai ō Tuhinapo in the last week.
In response to questions from RNZ, Oranga Tamariki deputy chief executive of youth justice services and residential care Dean Winter said one incident resulted in two young people being referred to police, and another involved staff responding to a young person who required de-escalation.
"The third involved alleged use of force by a staff member in relation to a young person's behaviour, and we can confirm this is being investigated."
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Winter said in all instances the wellbeing of those involved was a priority, with medical checks provided where needed.
"Oranga Tamariki provides regular, ongoing training for staff, and residence management provide a range of support for kaimahi involved in incidents, including sharing learnings about the response."
Winter said young people placed within a youth justice residence may have been sentenced by the court due to their offending, or may be remanded in custody while waiting for a court date due to alleged offending.
"This means that the cohort of young people within a residence change frequently, which can alter the dynamics of each unit. Managing these complex dynamics, while supporting the rangatahi, is part of the operational challenge in our residences."
RNZ earlier revealed there had been two other incidents at the facility, near Rolleston, last month.
At the time NUPE union secretary Janice Gemmell told RNZ they were "preventable" and a "real concern".
"The incidents are serious - staff are suffering serious head injuries and other injuries and it is unacceptable.
"NUPE has been aware of ongoing harm to staff and has raised concern and solutions to the highest levels."
Gemmell said there were a series of concerns being raised by members, including concentrations of young people with high and complex needs, low staffing and risk of ongoing harm to staff and young people.
"NUPE has been continually raising concerns about risk and staffing numbers. We do not want to see members seriously hurt or killed at work."