A prisoner who escaped the custody of Corrections staff at Waikato Hospital in Hamilton was there for "medical oversight".
Police were notified about 1.30pm that a prisoner had escaped from Corrections custody at the hospital on Pembroke Street.
A spokesperson said police officers were actively searching for the escapee.
Corrections said the prisoner was on remand at Spring Hill Corrections Facility and escaped while on a visit to Waikato Hospital, details of which they were not able to release due to privacy.
Springhill general manager Scott Walker said the prisoner was handcuffed and wearing a GPS monitor when he escaped.
Walker said police were informed immediately and began a search.
He said public safety was the prison's top priority and any escape was unacceptable.
An immediate review into how the incident occurred would be carried out, Walker said.
A Corrections spokesperson would not say how many staff were escorting the prisoner when he escaped, but said none were injured.
A Health NZ spokesperson would not say whether any hospital staff or patients were injured or threatened.
Police said anyone in the immediate surrounding area who had seen anything suspicious should call them immediately on 111.
Police would not say whether the prisoner was considered dangerous and said the man's name and photograph would only be released if police planned an appeal for sightings.
They said the police Eagle Helicopter was not involved in the search.
It is the second time in a month that a prisoner has escaped from Waikato Hospital.
In the first incident in November, a prisoner escaped after allegedly assaulting two Corrections officers and carjacking a vehicle. He was later arrested.