Canterbury District Health Board is investigating how a mental health patient ended up spending two nights locked in a maintenance shed.
The patient at the troubled Hillmorton Hospital was reported missing just before Christmas and was found two days later in the shed.
RNZ was alerted to the incident by a source close to the story who said the patient was physically fine when he was found.
He had managed to keep himself warm and happened to have some sugar sachets on him which were his only source of sustenance during the ordeal.
The shed is used to store gardening implements, including a tractor.
RNZ has been told the man has a reasonably serious mental health condition and it is fortunate he didn't end up harming himself while being locked in the shed.
In a short statement the DHB's chief of psychiatry, Peri Renison, confirmed the man went missing and was later located in the maintenance shed which was on the grounds of the hospital.
"We are investigating the event to understand how this occurred so we can put measures in place to minimise the chance of a recurrence", Dr Renison said.
The statement notes the patient was from an open unit within the hospital meaning they were free to come and go.
RNZ was told no further comment would be made while the investigation took place.
Just before this patient went missing, the head of the DHB, David Meates, met with staff at Hillmorton to hear their fears somebody might be killed by a patient following a string of assaults on nurses.
These have escalated in the past year and include a nurse being hospitalised for burns after having boiling hot water thrown on them.
Staff who had spoken to RNZ anonymously said overcrowding at the facility, which had been running at above full capacity, had contributed to tensions along with a lack of experienced nurses.
In response, the DHB had boosted the number of security officers working there to five.
A new acute inpatient unit with eight beds is opening in March, which was expected to ease some of the pressure.
Mr Meates had previously commented on mental health services in Canterbury catering for twice as many people than before the earthquakes and the lack of facilities available to cater for them.