The Waitemata District Health Board (DHB) is investigating how a man admitted to the hospital managed to run away.
Adam Tan, 22, has not been seen since leaving it on 27 October.
Police are trying to formally identify a man's body found in a stream by a member of the public behind Trust Stadium in Henderson - near the hospital - about 10.30am today.
The body has been removed from the stream and formal identification and a post-mortem will take place tomorrow.
Police would not confirm any more details until then, and could not say whether the body was that of Mr Tan.
A Waitemata DHB spokesperson said it had launched an investigation into how Mr Tan, who had been admitted to the hospital, was able to run away.
Officers spent Friday searching for Mr Tan in bush areas around the hospital, Henderson Creek, Central Park Drive and the Tui Glen Reserve. They had concerns for his welfare due to his state of mind on the morning he went missing from the hospital.
A police spokesperson could not confirm whether there were any suspicious circumstances surrounding the body's discovery.