A Police media spokesperson said the scene investigation was still ongoing and they would release an update if there were any significant developments.
The man was found in a garage about 4pm on Wednesday and taken to hospital, Detective Senior Sergeant Kim Libby, of Waitemata CIB, said.
Hospital staff told police later that day about the man and initial inquiries by police appeared to indicate the injuries were accidental, Libby said.
Several police vehicles remain in Verran Rd, Birkdale.
"However, as a result of further information received from medical staff this week, police are now treating the injuries as unexplained," she said.
"Police are currently working to establish the exact circumstances around how the man received his injuries and a team of officers will be carrying out a number of inquiries in the Birkdale area over the coming days."
• Anyone who may have noticed anything suspicious in the area surrounding Verran Rd on Wednesday afternoon, or anyone with any information that could help police should call Waitematā Crime Squad on 09 839 0697 or Crimestoppers on 0800 555 111.
