New details on mother missing after giving birth near Sydney river

Emergency services were called to Cooks River at Earlwood in southwest Sydney on Monday afternoon after a resident walking his dog found what he believed to be a placenta and umbilical cord.

Police say tests on the organs revealed them to be human and have now confirmed the baby is male.

Serious concerns are held for the welfare of the mother and boy and police are still urging the mother to contact authorities.

A search around the Cooks River on May 28 failed to lead to a breakthrough after police zeroed in on an area they felt needed further investigation.

Burwood Detective Chief Superintendent Christine McDonald said she was "deeply concerned" for the safety and mental health of the mother and the safety of her baby.

"Childbirth for many people can be a traumatic time and it can be very distressing," she said. "I need to know she is safe."

Supt. McDonald said they have "located an area that needs further investigation".

She said "how the placenta and umbilical cord became detached is part of our inquiries".

"We do know it is human blood," she said. "The mother would be in some form of discomfort."

The Cooks River flows from Yagoona in Sydney's outer southwest and runs into Botany Bay at Kyeemagh, 23km away. It is heavily polluted as a result of traffic congestion, litter, sewage, illegal dumping and industrial and domestic activities.

Supt. McDonald said lights were brought in to allow the launch of a large-scale search on Monday night.

"Obviously our search will hopefully identify what has taken place; whether the delivery of that child occurred at this location or another location is yet to be determined," she said.

"I ask anyone with information to contact Crime Stoppers.

"It's very important and it's extreme urgency we find the mother and the child as soon as we can. We ask she goes to a hospital. We will be contacting hospitals."

Anyone who has information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at nsw.crimestoppers.com.au