Search continues for mum after riverside discovery

Authorities have been searching for the woman and baby since the discovery of a placenta and umbilical cord near the Cooks River at Earlwood in Sydney's southwest.

The woman has been urged to immediately seek care at the closest hospital, with authorities insisting she is not in trouble and there will be no judgment, amid concerns for her and the baby's health.

The mother's identity and whereabouts remained unknown more than 24 hours after the discovery as police concluded a search of the river area.

NSW Police are racing against the clock to identify her, Superintendent Christine McDonald said.

"Time is very important in this scenario," she told reporters on Tuesday.

"We do want to know who she is, because we want to know that she is safe and that she is receiving the support and the medical help that she needs," she said.

Police divers and a blood-detection dog were involved in the large-scale search, yielding only a false alarm when a recently buried cat was discovered among the mangroves.

Expected results of forensic testing on the placenta and umbilical cord might identify the baby's birth date and gender, but it was not clear how they got by the river or how long they had been there, Supt McDonald said.

A dog-walker reported the find to police on Monday afternoon after coming across the scene, not far from a busy footbridge across the river.

The riverside site is less than 4km from Canterbury Hospital.

Police have appealed for anyone who may have seen a distressed or pregnant woman in the vicinity to contact authorities.

The Cooks River flows from Yagoona in Sydney's outer southwest and runs into Botany Bay at Kyeemagh, 23km away.

Sections are heavily polluted as a result of traffic congestion, litter, sewage, illegal dumping and industrial and domestic activities.

Australian Associated Press