Prime Minister Christopher Luxon has described the case of an 11-year-old girl being mistaken as a 20-year-old woman and put in a mental health unit as "extremely distressing".
"As a parent, you identify with what is a horrific set of circumstances... it's just incredibly distressing and concerning," Luxon told reporters at Parliament.
"Massive amounts of empathy and concern for her and her family."
Health NZ has apologised over the incident, in which the girl was handcuffed by police officers and taken her to Waikato Hospital's Henry Bennett Centre.
Luxon said it was "unacceptable" that Health NZ took two weeks before informing Health Minister Simeon Brown.
"There's now an inquiry under way, I know it's got the full attention of Simeon Brown, he's all over it."
Asked whether heads should roll, Luxon said: "By all means, there should be accountability in the system."
Police Minister Mark Mitchell said officers were "doing the best that they could" to look after the girl during the incident.
He told reporters the "perfect storm" occurred after police recovered the girl from the railings on a Hamilton bridge and took her to Waikato Hospital.
"All our police officers were trying to do was care for an 11-year-old that was out on the streets, that was non-verbal, that was standing on a bridge with who knows what the intent was.
"The police, unfortunately, throughout the process, have misidentified her, but make no mistake, they were doing the best that they could to look after her and to support her."
Mitchell said he expected police to carry out their own review of the mistake, as well as taking part in a separate Health NZ review.
The Chief Children's Commissioner Dr Claire Achmad said she was very concerned over the incident.
“I am thinking of her and her whānau while they navigate the aftermath of what has occurred," Achmad said.
"I am pleased to see reported in the media that both the Police and Health New Zealand have acknowledged mistakes and committed to a full review. It is essential that any review and response puts this child’s rights and specific needs, wellbeing and interests at the centre, and supports her active participation.
Labour leader Chris Hipkins said he wouldn't be politicising the case, as the government of the day was not responsible.
"It's clearly a major mistake... this could've happened under any government," Hipkins said.
"It's utterly unacceptable, and I do think they need to get the bottom of exactly what happened as quickly as they can and provide some reassurance to the New Zealand public that this won't happen again."
Hipkins said it was "very concerning" that ministers weren't advised by their officials more promptly.
"I'd be having some very stern words with a range of government departments, be pulling them all in actually to find out exactly how this happened."
