The treatment of a maximum security prisoner who was frequently tied to a bed for significant lengths of time is being investigated.
The inmate, described as a "difficult prisoner" at the maximum-security Auckland Prison, tried to harm himself three times in a week in February before the preventive measure was put into place said a statement released by the Department of Corrections.
The duration and frequency of the restraint were a cause for concern, said the Department of Corrections chief executive Ray Smith.
He said the Office of the Ombudsman, which is an independent body, had raised the alarm and, as a result, he ordered the chief inspector of Corrections Andy Fitzharris to investigate.
"The Department is committed to preventing unnatural deaths and life threatening incidents of self-harm in prisons but despite our efforts to reduce suicide and self-harm in prison it is incredibly difficult to stop someone who is determined to harm themselves.
"I decided to initiate this review given the length of time and frequency in which it was deemed necessary to use a tie-down bed in this prisoner's treatment, and concerns expressed to me about this by the Office of the Ombudsman."
The extensive investigation, which is expected to conclude next month, will review a number of factors, Mr Smith said.
Corrections is also undertaking a review into the policy, guidance and training related to the use of tie-down beds.