A neighbour says they heard what sounded like arguing and loud noises in the lead up to a newborn baby being found in a backyard in Keilor Downs, in Melbourne’s north-west, this morning.

Police said a resident found the baby on their property just before 8am, and that a woman was later located at a nearby address.

Both she and the baby were taken to hospital for treatment.

Ambulance Victoria said Advanced Life Support and Mobile Intensive Care paramedics attended, but both the infant and the woman were in a stable condition.

The Brimbank Sexual Offences and Child Abuse Investigation Team is investigating the incident and detectives and forensic investigators remained at the scene throughout the day.

Two people in orange overalls near a blue SES tent on a footpath behind police tape beside a police car on a cloudy day.

Emergency services remained at the scene throughout the morning. (ABC News: Alexandra Alvaro)

One person who lived on the street said they heard what they believed was “multiple people” arguing and loud noises coming from one of the homes before there was a loud bang.

They said they did not know something serious had happened until they received a call about police being in the street.

Another local, Arzu Irgat, said she could see a police tent set up in the backyard of the neighbouring home.

“Poor baby, we are saddened that such a disturbing event happens so near by,” she said.

“I wish mum and baby are all good.”

An orange tarp hangs between a brown tiled roof and a blue tent that has "SES" written on it and extends over a fence.

Police have spent the day examining the backyard of a Keilor Downs property. (ABC News)

Resident Michael Tait said he also heard a sharp bang followed by an emergency vehicle arriving outside with its lights and siren going.

“I could see all this activity just next door,” he said. 

“Three police cars, an ambulance, someone was getting put into the ambulance … and plenty of police walking around.”

He said he was unaware a baby was involved.

A man with white hair, beard and glasses in a blue polo shirt stands in front of a brick house with his hands behind his back.

Michael Tait said he saw police and paramedics in the street but was unaware the incident involved a baby. (ABC News: Alexandra Alvaro)

Seff Fajardo said he was leaving his home when he saw the police and ambulance in the street.

“I feel awful … it’s terrible,” he said.

“People were going around and checking sides of the houses.”

Microphones point at a man with a dark beard in a black cap and shirt, both with orange writing, standing on a street corner.

Seff Fajardo says he saw police and paramedics in his street. (ABC News)

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or www.crimestoppersvic.com.au.