The woman who left a dead newborn baby in a South Auckland park would be showing signs that something was wrong, says a women's health expert.

Police continue to search for the baby's mother after the body of a baby was found on Hastie Avenue Reserve in Mangere Bridge yesterday morning and concerns are growing for her well-being.

Appeals have been made by police and local politician Sua William Sio for anyone with information to come forward in confidence.

The area where the baby was found is under a cordon and a post-mortem examination on the newborn was due to take place this morning.

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Police are attending the scene on Mona Avenue, Mangere, where the body of a very young baby has been found.

The executive director of a Wellington post and ante-natal distress support group Antoinette Ben told Newstalk ZB's Mike Hosking given the tragic circumstances the woman would have been terrified at the prospect of having a child.

She said it could be related to age or culture though there were any number of reasons leading to a new mother taking such drastic actions.

"She might have been obviously not prepared to have this baby, maybe didn't realise for a long time that she may have been pregnant or hidden it. Obviously it was incredibly terrifying for her to think about having this baby and keeping it so it could be cultural or it could be fear of what her family might do or say."

She said there would have been signs to those closest to the pregnant woman that something was wrong.

"I think it depends on what is going on for that person at the time. I'm sure that there would have been signs but as humans we're pretty good at hiding things especially if we feel like it's not going to be accepted."

But given it was 24 hours after the grisly discovering there were increasing concerns for the well-being of the mother.

"Obviously she's had this baby and she would need medical attention but also how traumatic would this event been for her - massively traumatic - and I really feel for her and I just really hope she gets the support she need."