A blood detection dog has joined the search along Sydney’s Cooks River as police continue to look for a woman believed to have given birth on the riverbanks on Monday.

The desperate search for the mother and newborn baby was in its second day on Tuesday, as NSW Police said they held “serious concerns for the welfare of the child and its mother”.

“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,” Superintendent Christine McDonald said.

“It’s very important and it’s extremely urgent that we find the mother and the child as soon as we can.

“We ask she goes to a hospital. We will be contacting hospitals.”

Shortly before 10am on Tuesday, McDonald said a new site had been found in mangroves, and crime scene investigators had been recalled. She did not say what drew police attention to the particular site, but said a blood detection dog would be brought in.

“It’s particularly muddy down there,” she said.

The search along the river began late on Monday after the discovery of a placenta and umbilical cord on the banks at Earlwood, about 10 kilometres south-west of the city centre.

Emergency services were called to the site, near a popular riverside walking track, after a resident walking his dog found evidence of a birth. Tests on the placenta and cord revealed they were from a human.

There was a large-scale search of the area overnight, with a spot near Lang Road remaining taped off on Tuesday.

Investigators were also searching a grassy area outside the Canterbury Rugby Union Club.

The nearby footbridge over the river is heavily used by local walkers, joggers and cyclists.

The site is less than four kilometres from Canterbury Hospital.

McDonald said lights were brought in to allow the search to continue on Monday night. Police divers arrived early on Tuesday.

Police did not yet suspect the baby was in the river, McDonald said.

“At this stage our main concern is for the whereabouts of the mother and the child,” she said.

“We are doing everything we can and that’s why the appeal is to come out – we see that as a really urgent matter for us to find her and her child, hopefully safe and healthy.”

McDonald said there was no judgment involved in the investigation.

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

“Childbirth presents a number of health concerns, hence why we are requesting the mother goes straight to hospital and speaks to health professionals.”

The Cooks River flows from Yagoona in Sydney’s outer south-west and runs into Botany Bay at Kyeemagh, 23 kilometres away.

Sections are heavily polluted due to traffic congestion, litter, sewage, illegal dumping and industrial and domestic activities.

Recent Sydney clean-up campaigns have focused on the waterway, while low-lying sections have also been susceptible to flooding.

-with AAP