Health NZ says it is investigating in depth as to how an 11-year-old girl was taken to a Hamilton mental health facility in a case of mistaken identity. 

She was mis-identified as a 20 year old patient seen climbing Fairfield Bridge's railings - then cuffed and injected with antipsychotic drugs. 

Health NZ Deputy Chief Executive Cath Cronin says they're deeply sorry and are working with the family. 

She says there is much she can't reveal at present.

"We need to really understand what's happened here - and I've got to wait for the review to get down into the absolute details of what's happened."

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