Heavily armed tactical response police carrying assault rifles have surrounded the front of an industrial estate in Sydney's southwest, where an armed man is holed up after a triple shooting.
Police have confirmed one man is dead and two other men are in hospital after the shooting at Ingleburn at about 10.45am on Monday.
One person has been arrested and led away in handcuffs but an armed gunman remains inside a building at InLine, a signage business.
"On arrival, police found three males - one deceased and two with gunshot wounds," NSW Police said, Sky News reported.
"The deceased is 43 years old. One man is undergoing emergency surgery, the other has superficial wounds to the lower part of his body."
Police said it was a delicate operation and were unable to provide more information.
"At this stage there is an on-going investigation, tactical operations unit and negotiators are on scene and the operation is continuing."
Streets are shut down around the business and traffic is being diverted.
Witnesses from nearby businesses say they heard five gunshots ring out on Monday morning.
An ambulance was called to the industrial area at 10.45am and police have confirmed two men have been taken to hospital for treatment although their conditions aren't known.