A man has died at Whangārei Hospital after being restrained following an assault on a staff member.
Police had been called to the hospital's mental health unit just before 10pm yesterday, to help with an unrelated matter.
Detective Inspector Lloyd Schmid said while the police were there, another patient in the ward assaulted a staff member.
The man was restrained by police officers and hospital staff.
The man became unresponsive and CPR was carried out, but he died shortly after midnight, Mr Schmid said.
Police said they were working with the Northland District Health Board to investigate what happened.
"A scene examination is currently underway and as part of our enquiries, police will be talking to those involved at the scene as well as any witnesses to this incident to establish what has occurred," Mr Schmid said.
A post-mortem examination will be carried out tomorrow.
Police are working with the family of the dead man and providing them with support.
Both the Independent Police Conduct Authority and Worksafe have been notified.