A man from Wairoa is in an induced coma after being found lying in a ditch in the town on Tuesday morning.
The 19-year-old being treated for head injuries in Hawke's Bay Hospital.
Detective Sergeant Steve Smith says police have no idea whether the man was assaulted or had been in some sort of accident.
Mr Smith says before a member of the public found the man he been seen wandering around in a distressed state.
Police in Wairoa are keen to hear from anyone who saw suspicious or unusual activity near Lambton Square Memorial park.
