A major search is underway for a mother and newborn baby after the discovery of disturbing “evidence of a birth” on a riverbank in Sydney.

A man walking his dog found what appeared to be an umbilical cord and placenta on the Cooks River, Earlwood, about 4.30pm Monday.

Forensic testing confirmed the worrying find was from a human.

NSW Police said they held grave fears for the mother and child as it appeared the woman had given birth on the riverbank.

Police urged the woman to go to her nearest hospital to ensure she got urgent care for herself and the newborn child.

A crime scene has been established and a police investigation launched.

On Tuesday morning, police divers and boats were combing the waters of the river in Sydney’s south-west. Officers had also spent the previous night searching the water’s edge on foot.

Detective Chief Superintendent Christine McDonald said emergency services were called to the scene after a man found “signs of a birth”.

“Police arrived and spoke to the passer-by and subsequently we’ve conducted some forensic examinations over the last couple of hours,” McDonald said on Monday night.

“I can confirm that a placenta and an umbilical cord of a human has been located.

“It is very important and it is extreme urgency that we find the mother and the child.

“All we know is that a placenta and umbilical cord was located.

“Obviously, our search undertaken will hopefully identify what has taken place.

“Whether that birth or the delivery of that child occurred at this location or another location is yet to be determined.”

Police are appealing for information. Anyone with CCTV vision or information about the incident is urged to contact contact Burwood Police or Crime Stoppers on 1800 333 000.