Police are treating the shooting of a man at Prairiewood in Sydney's west as an attempted murder and say they believe it was gang related.

The 24-year-old is in a critical condition after being shot in the back outside his home in Nugent Place at Prairiewood.

The man was known to police, who moved to reassure residents who were concerned about the attack occurring in a suburban street.

"It is concerning but I would reiterate this is a targeted attack, they're not general members of the public," Superintendent Peter Lennon said.

"We're working with the Middle Eastern organised crime squad and homicide squad to get to the bottom of it."

Neighbours told the ABC they heard three bangs at the time of the shooting about 10:25pm on Thursday.

The victim called triple-0 and police found him on the doorstep of his house.

"His mother was home at the time and she came out and helped him," Superintendent Lennon said.

A single bullet had entered one of the man's lungs and he underwent emergency surgery at Liverpool Hospital this morning.

He has not provided information about his attacker, or attackers, and his mother told police she had not seen anything.

Search for gunman

The suspect has only been described as male with black hooded jacket.

Detectives looking for the gunman were interviewing local residents today.

"From what we understand there were only three shots fired, one of which hit the victim, so we may look at only one shooter or we may look at possibly others depending on what comes back from the canvas," Superintendent Lennon said.

"It is a dead-end street so we believe whoever was responsible for firing these shots was on foot, so we've had to extend the canvas and look at a number of other streets in surrounding areas to find out what occurred."

Police were hoping the victim would provide more information later today.