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.