Sydney dog walker Tony Robson makes a shocking discovery in bushes beside Cooks River at Earlwood - sparking a massive ongoing police hunt

A dog walker has revealed the shocking moment he discovered an umbilical cord and a placenta on a muddy riverbank, as the search for a mother and her newborn baby continues. 

Local resident Tony Robson found the body parts hidden in some shrubs near the banks of the Cooks River at Earlwood in Sydney's inner south-west at about 4.30pm on Monday, while he was walking his dogs. 

Mr Robson and his wife alerted police to the discovery of the organs before emergency services arrived at the scene a short time later. 

'It was just sitting on top of the mud, the water was quite a distance away,' he told 7 News.

Mr Robson, a father, said he immediately recognised the placenta and the umbilical cord. 

[I've] seen three births so you kind of know what you're looking at,' he said. 

'I couldn't think what else it could be. It looked about the right size for a human. 

'My wife took a photo of it, and we called the police.'

NSW Police continue to investigate the incident and hold grave fears for the safety of the mother and her child. 

Police have urged the woman to go to the nearest hospital to seek medical attention for herself and her baby.  

A crime scene was set up yesterday as a major search for the mother got underway with the help of rescuers including divers. 

A blood detection dog is also assisting in the large-scale search and rescue effort,  after the woman and child could not be located on Tuesday. 

Police were seen scouring another area of interest near the riverbank and sealed off the area with a blue tarpaulin. 

Investigators initially identified the area as a place where something appeared to have been buried, but the search was discontinued after it was deemed to be a false alarm. 

NSW Police Detective Chief Superintendent Christine McDonald did not rule out the likelihood the baby may have been placed in the water. 

Police have not found any evidence to indicate the child was harmed. 

Superintendent McDonald said on Monday night the priority of police is to ensure the mother and her child are located. 

'At this stage our main concern is for the whereabouts for the mother and the child, we see that as a real urgent matter for us to find her and her child, hopefully safe and healthy,' she said. 

Superintendent McDonald said police are not judging the woman and they are only looking out for her welfare. 

'They need to know we are concerned for them, that we are wanting to know that they are safe,' she said.   

Anyone who lives in the areas of Wardell Road and Lang Road areas of Earlwood, or Tennant Parade, Hurlstone Park and Ewen Park who may have seen a pregnant woman in distress, has been urged to contact police or Crime Stoppers on 1800 333 000.