A major police operation is under way after a shooting outside a shopping complex in Sydney’s south-west, with eyewitnesses describing the moment a man ran for his life after masked assailants fired several gunshots outside a gym before making a swift escape.

Police swarmed a car park on Steer Road, Gregory Hills about 8.35am on Friday, finding a number of bullet casings. No injuries were reported, and police believe the man who had been targeted left the scene immediately.

Police respond to reports of a shooting in Gregory Hills on Friday.

Police respond to reports of a shooting in Gregory Hills on Friday.Credit: Nine News

Two armed assailants dressed in balaclavas and dark clothing are believed to have shot at the man, and remain at large after fleeing the complex.

A car park adjoining a shopping centre on Steer Road, which includes a World Gym and Service NSW, has been blocked off by police tape and emergency vehicles.

Detectives were photographed interviewing one person outside an entry to World Gym, which is part of the exclusion zone marked by police. A black ute has blocked movement on the road leading out of the car park, while several traffic cones are placed in the restricted area.

One witness, Lucas, told 2GB he saw two people with balaclavas and armed with handguns enter the shopping complex and fire eight or nine gunshots.

“There seemed to be someone running but by the time I could get a description, I had already fled,” said Lucas, who was putting out stock at his shop when the shooting occurred.

Police cordon off an area of the car park outside World Gym.

Police cordon off an area of the car park outside World Gym. Credit: Nine News

Another witness, Jack, counted 10 shots of “rapid fire” from the Service NSW on Steer Road. He called 2GB from a secure room inside the store, where he had gathered with other customers and staff members.