The mother of a dead baby girl discovered at a Hutt Valley property has been found.

Police say they located a woman in her early 20s during a canvass of the area on Tuesday.

Inspector Shane Cotter says the woman hadn't sought any medical attention, but she has been hospitalised on Tuesday afternoon and is being treated for complications as a result of the birth.

The baby girl, who appeared to be no more than 24 hours old, was found on Monday wrapped in a towel at the back of a property in suburban Taita by a woman who had gone outside to hang the washing.

A post-mortem examination is expected to be carried out on Wednesday.

It's hoped this will determine whether the baby was alive at the time of her birth or not.

Police had been concerned about the mother's wellbeing, because they had not been able to locate the placenta and the baby still had part of her umbilical cord attached.