POLICE fear there could be violent reprisals in Sydney's west after four men were gunned down in what is believed to be an attack by a rival group.

The men, aged between 20 and 25, were shot outside a Smithfield residence just after 8pm (AEST) on Friday.

About 15 bullet holes were found in a garage door at the property.

The victims were currently undergoing surgery on Saturday for non-life threatening injuries, including gunshot wounds to the stomach and leg.

Police have said the shooting was targeted, but have ruled out any links to outlaw bikie gangs.

Acting Assistant Police Commissioner Arthur Katsogiannis said the shooting "relates to a conflict between groups which are known to police".

He said police were worried about reprisal action in the wake of the shooting.

"Certainly, we're concerned about retaliations," Mr Katsogiannis told reporters on Saturday.

"We'll be working very, very closely with the local area command investigators to ensure that we target those areas and individuals.

"We know who the individuals are in these groups."

Police were investigating the possibility that the incident could be linked to another shooting in the area on April 22, Mr Katsogiannis said.

He said a silver Holden Commodore was seen fleeing the scene shortly after the shots were fired on Friday night.

Police would be reviewing CCTV footage of the bullet-sprayed house.

Police hadn't yet spoken to any of the injured men, Mr Katsogiannis said.

The incident is one of seven shootings across the state in the past six days.

Mr Katsogiannis said he couldn't remember many worse weeks for crime in NSW.

"It's certainly one of the worst crime weeks we've had on record, it's very, very unfortunate in that respect," he said.

"Maybe it's the full moon, I don't know."