A man is to appear in Whangarei District Court on Saturday charged with the murder of a young woman found dead in a stream in the city.

The 29-year-old man was arrested late on Friday, police said. The body of the 21-year-old woman, who was known to the accused, was found in Waiarohia Stream about 4.20am on Friday.

An autopsy has been carried out in Auckland but police have yet to confirm her identity or cause of death.

Detective Senior Sergeant Dene Begbie appealed for witnesses of suspicious activity in the Tawera Road area around the time of the murder to come forward.

"Someone may have seen something unusual that has caught their eye or noticed suspicious activity around Tawera Road and Porowini Avenue. Any information could help us establish what may have happened before the woman was found in the stream."