The wife of the injured 25-year-old man is understood to have phoned triple zero after her husband was shot inside the home on Fantail Crescent at Erskine Park just before 9pm on Thursday.

Paramedics arrived to find the man suffering from multiple gunshot wounds, including to his back and arm.

They treated him at the scene, before taking him to Westmead Hospital, where he remained in a critical condition on Friday morning.

Officers from the St Marys Local Area Command set up a crime scene on the street overnight, as neighbours gathered around to watch. Police could be seen searching the front yard of the house, while the police dog squad also searched the street.

A NSW Police spokeswoman said the investigation was still in its early stages, and the circumstances surrounding the shooting were not immediately known.

Police could not immediately say whether they believed it was a targeted shooting, and no description of the shooter was given. No arrests have been made.

Anyone with information has been urged to contact Crime Stoppers on 1800 333 000 or use the Crime Stoppers online reporting page.

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