A man in his early 20s has been killed in a suspected targeted home invasion at his Glen Alpine residence, police said.

Emergency services responded at about 3.40am after the family called for help, and officers found the man with a gunshot wound. He died at the scene. Acting Superintendent Gretchin Atkins said multiple people allegedly forced entry and fled before police arrived, and that investigators believe the attack was targeted.

Atkins said a homicide investigation is under way with support from the New South Wales crime command’s homicide squad. A crime scene was established and forensics teams were working at the property. Police confirmed there were "multiple" alleged perpetrators involved, and she cautioned that investigators still had "a lot we don't know."

Police described the victim as not yet formally identified and said his family is assisting inquiries. Atkins said the man was only known to police for a traffic offence and otherwise had no known criminal involvement. Investigators are appealing to anyone who was in the area around the time of the attack, or who saw vehicles or people that might assist with inquiries.

Atkins also said officers were aware of a social media post by an alleged Sydney gangland figure claiming the shooting was a case of mistaken identity, but she stressed the loss of life was the immediate priority. "A young man has lost his life today and that's obviously just tragic," she said. "It's an active crime scene and we're obviously waiting for a lot of that information from our forensics who are on the scene."

The attack follows a fatal home invasion in Guilford three days earlier, in which a 28-year-old man was shot. Police made no suggestion the two cases were linked. The Glen Alpine case comes after other high-profile incidents this year, including the kidnapping murder of 85-year-old Chris Baghsarian, who was abducted from his home in Sydney's north in a case police described as mistaken identity.

The investigation remains active, alleged offenders remain at large, and police have called for public assistance as they pursue forensic leads and witness accounts.