A family that had moved in only a week earlier has told of finding an abandoned newborn baby in their backyard.

Police are worried for a mother who remains missing after the baby girl was found at a home in Blacktown in Sydney’s west on Friday.

Anna Carlos told The Daily Telegraph the child still had its umbilical cord attached and was shivering when they discovered it.

She described how her sister Lara heard faint cries while hanging out the washing on Friday afternoon.

The baby on their patio was only hours old, unclothed and still covered in birth fluids, the newspaper reported on Monday morning.

After making an emergency call, Mrs Carlos was told to clamp the umbilical cord, and all she could find was a shoelace.

“I couldn’t find anything in the kitchen, so I grabbed a shoelace and used that…then they (paramedics) talked me through how to do it,” she said.

Emergency services were called to the home on Friday afternoon where they found the infant, believed to be days old, and took her to Blacktown Hospital.

The baby is believed to have been left at the home between 12.30pm and 2.40pm on Friday.

Fears are now growing for the condition of the mother who has been missing for two days.

“We’re really concerned about her health,” Acting Inspector David McInerney from Blacktown Police told reporters.

“Childbirth can be quite traumatic and we’re worried for her safety and wellbeing, both physically and mentally. We’re trying to help her.

“It’s very concerning, but she’s not in any trouble from police. I want to stress that.

“We’re appealing to her to come forward, to get some help, and let us help her.”

The woman has been urged to attend a hospital, call an ambulance or attend a police station as soon as possible.

The baby remains at Blacktown Hospital on Saturday, and will be cared for by the Department of Communities and Justice after she is discharged.

Detectives on Friday gathered CCTV footage from neighbouring residents showing a car arriving at the home, which they believe could assist their investigation.

The location where the baby was left is believed to be “completely random” and had no connection to the mother, a police spokesperson told AAP.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.

-with AAP