By Megan Gorrey and Laura Chung
A 20-year-old man was shot dead after he allegedly grabbed a police officer's gun during a scuffle in the backyard of a home in Sydney's west.
NSW Police said four plain-clothes officers were on patrol near the St Marys Hotel on Queen Street in St Marys when they approached Bradley Balzan as he was "acting suspiciously" shortly before 10.30am on Wednesday.
Mr Balzan allegedly fled from police and scaled the back fence of a house a few blocks away on Acacia Avenue before threatening two of the officers who followed him.
Police said a scuffle broke out and Mr Balzan had grabbed one of the officers' firearms, before the second officer shot the man in the stomach.
Paramedics and the officers tried to save Mr Balzan but he died at the scene.
One of the officers, a male senior constable, was treated in hospital after he was bitten by a dog during the confrontation.
Bradley Balzan, 20, was fatally shot in the stomach during a confrontation with police.Credit: Facebook
NSW Police Assistant Commissioner Mark Jones said it was not clear whether the police officer’s gun was holstered at his waist or being held in his hand when Mr Balzan got hold of it.
“Police will allege the weapon was in the process of being taken from the deceased and one shot was discharged from that firearm.”
“Tragically, unfortunately, that male has died as a result of that gunshot wound.”
He said he did not know what it was about the man's behaviour that made police believe he was acting "suspiciously".
Police and emergency crews at Acacia Avenue in St Marys.Credit: Nine News
Assistant Commissioner Jones said the police involved were “put into a very confronting situation” and were receiving welfare support. He said the officers were “experienced” and at least two were senior constables.
“It’s a very sad set of circumstances anytime, particularly towards Christmas, so our hearts go out to the [man’s] family," he said.
The police homicide squad will investigate the circumstances surrounding the shooting, which has been declared a critical incident.
That probe will be subject to an independent review overseen by the Law Enforcement Conduct Commission.
The man's death will be referred to the coroner.
Police were continuing to scour the residential street, a large section of which had been taped off, and the backyard of one house on Wednesday afternoon.
Earlier, an ambulance was in the street and a police riot squad vehicle was parked on the grass opposite homes.
Acacia Avenue is a couple of blocks behind the main St Marys shopping strip on Queen Street. Police urged members of the public to avoid the area.
In October, a NSW Police officer fatally shot a man who police allege pointed a double-barrelled longarm gun at officers when they stormed a house on the Central Coast following a high-speed pursuit over a stolen vehicle.
During an unrelated incident in April, police shot dead a 51-year-old man after he allegedly threatened officers with a meat tenderiser and a hammer at Rockdale in Sydney's south.