A man who was shot in the face with pellets in Sydney's southwest was outside a Shia Muslim prayer hall, which had reportedly received threats just hours earlier.

The 47-year-old was standing outside the fenced-off building on Rosedale Ave, Greenacre, just after 1am today when a number of shots were fired, police said.

It's reported Shia worshippers inside the hall heard the shots and then dragged the man inside the building before paramedics arrived at the industrial area.

It is believed the attack may have been motivated by the sectarian conflict in the Middle East.

A friend of the victim said threats by alleged Islamic State supporters had been made during the evening, before the shooting.

"They drive past, they stop here, they make threats 'Isis lives forever' this and that," he told ABC Radio.

The victim, who was shot in front of his family, received pellet wounds to his face and shoulder, and is expected to undergo surgery.

The injuries are not believed to be life threatening.

Local employees were shocked when they arrived at work on Monday to find Rosedale Ave a crime scene and cordoned off.

They said the prayer hall was usually a very quiet place.

"That place has been open since 2004. It's the first time we've ever come across something like that," an employee from a nearby car business told AAP.

"Usually it's pretty quiet during the week. Maybe it gets a bit busy on Friday if they have something special."

It's believed the worshippers were gathered to commemorate the death of Imam Hussein, a grandson of Prophet Mohammed, and one of the most revered figures of Shia Islam.

The employee said police had taken the CCTV footage from his workplace.

Police are unsure what led to the attack.

"At this point in time it does not appear that there is any type of motivation for the shooting," Inspector Dave Firth said.

It remains unclear if the shots were fired from a passing vehicle.

Police spent this morning combing the area for clues.