The remains were discovered by children playing in the creek at 6pm yesterday near the Stanmore Bay Leisure Centre, 40km north of Auckland.
Detective Inspector Bruce Scott said police were investigating who the person was and how they got there.
"It would appear they have been there for quite some time as they are quite decomposed. So far we are only in the early stages of our investigation."
A pathologist was at the scene and the body would be removed from the creek and taken for a post-mortem and identification today.
Mr Scott said the remains had probably been there for weeks or months and said there was always a possibility it could be mother of two, Alanah Brough , 39, who went missing on January 30.
"Until we have identified the body we won't know for sure if it is this missing woman.
"She hasn't been sighted since she went missing. This has been an on-going missing persons investigation we have been following closely."
As part of their inquiry, police will talk to all those who have seen the body .
The creek where the body was found is in a rugged swampy area very close to houses.
Mr Scott said there was no cause for concern for nearby residents.
