Revenge attacks are feared after a religious leader was shot in the face outside a Sydney Shia Muslim prayer hall hours after it had received threats from Islamic State supporters.

Rasoul Al Mousawi was standing with his family outside the Husainiyah Nabi Akram centre in Greenacre just after 1am on Monday when a number of shots were fired.

Shia worshippers, including women and children, had spent the evening at the hall during the holy month of Muharram.

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Mr Mousawi, 47, received pellet wounds to his face and shoulder and is expected to undergo surgery.

The injuries are not considered life-threatening.

Worshippers said threats about ISIL had been made during the night of the shooting.

The prayer hall on Rosedale Avenue. Picture: Google Maps

“They drive past, they stop here, they make threats ‘ISIS lives forever’ this and that,” one caller told ABC Radio.

Tensions are fierce between ISIL supporters, who are Sunni Muslims, and their rival Shiites.

Local activist Jamal Daoud said he had heard talk of revenge attacks being planned.

“This is very dangerous,” he said.

“It’s a warning something bigger could happen.”

Mr Daoud, of the Social Justice Network, said the prayer hall had been targeted before but says worshippers will not be deterred.

“This will scare people, but people will still go,” he said.

The victim’s daughter said her father was shot from behind as they were leaving the hall.

“My dad just held his neck and ran inside,” she told Network Ten.

“All I see was blood running down his head and neck.”

She described the shooting from behind as “really low”.

“If you had the real courage, you would have actually came to his face and did it,” she said.

The hall, which has been established for about a decade, is in an industrial area.

“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. The place is mainly used on the weekends.”

He said police had taken CCTV footage from his workplace to help gather evidence.

Police are unsure what led to the attack, which comes amid heightened tensions and follows the raising of the terror threat level to high in September.

Other Shia centres have also increased their security presence in the light of threats.

Police spent Monday combing the Greenacre street for clues.

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