Police said the handcuffs were immediately removed and staff performed CPR until an ambulance arrived on scene.
The man was pronounced dead at the scene.
Area Commander for Western Bay of Plenty Police, Inspector Clifford Paxton said an investigation is underway on behalf of the Coroner in relation to how the man died.
"As a matter of procedure in these cases an Independent Police Conduct Authority investigation has also been initiated," he said.
"Police are in contact with the man's family and will continue to liaise with them to ensure they receive the necessary support and are kept informed."
Until the investigation into the man's death is concluded it is inappropriate for police to comment further.
Police said no further details of the man who died will be released until he has been formally identified and police are satisfied that all family members have been notified.
A post mortem will be carried out to establish the cause of death.