Police have said they do not think a six-hour armed siege in Sydney’s south west was related to outlaw motorcycle gangs, as the father of the alleged gunman was charged.

Suspected gunman, Wayne Williams, 33, shot at three brothers, and held three bystanders hostage in the siege at Inline National Signage, in an industrial complex, on Monday morning.

Michael Bassal, 43, was killed after he and his two brothers, aged 41 and 34, arrived at the workshop. The two brothers were also shot with a semi-automatic weapon but survived.

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The siege ended when the alleged gunman fatally turned a gun on himself.

Police said the incident did not seem to be related to outlaw motorcycle gangs, although some of the people involved were members of clubs.

They described it as a “business dispute”.

Michael Bassal, 43, died after being allegedly shot by the gunman. Photo: Facebook

Wayne Williams’ father Peter, 52, has been charged with discharging a firearm in a separate shooting earlier in the day.

He and a 30-year-old woman were charged with not assisting police with their enquiries.

The pair were taken out of the area by police by force early on during the siege.

Heavily armed police surrounded the building at an industrial estate in Health Street after the shooting started.

Officers said Michael Bassal, 43, was shot dead on the grass verge when he went to the premises. His two brothers were taken to Liverpool Hospital and the 41-year-old man had to undergo emergency surgery.

Police said the younger man suffered minor injuries.

A hospital spokeswoman said both were in a stable condition at the hospital.

Three hostages were held for six hours as police tried to resolve the situation with the gunman, Wayne Williams, 33.

Police confirmed officers went into the building after 5pm and found the three factory workers hiding inside.

“Specialist police entered the unit where they located three persons, factory workers, hiding in that unit,” Detective Inspector Mark Brett from Macquarie Fields Local Area Command said.

“Further search of the unit located a male deceased.

“It is believed that that person died from a self-inflicted gunshot wound.”

‘Argument then rapid gunfire heard’

Earlier, witnesses reported hearing a loud argument before a series of rapid gunfire. This came before people could be seen fleeing the area.

Other witnesses reported hearing at least five separate shots fired.

Television crews who were filming the incident were told by police to stop, for fear the alleged gunman was watching live television footage inside the building.

The three hostages  freed just before 5pm left the scene unharmed.

The immediate area around the signage business was evacuated and members of the public were warned to stay away.

A man is led away from the scene by officers. He allegedly hindered police. Photo: AAP

Police said they did not believe the shooting was terrorism related.

A man who worked in the building complex where the shooting took place said he heard a loud bang, which he later realised was a gunshot.

He said police then evacuated his office and others in the building.

The man said he was sheltering with about 30 other people at a nearby business under police protection.

Rogan Burns, who works at an entertainment agency about 50 metres from where the shootings took place, said the whole area was in lockdown.

“My colleague actually left to go and get the boss a cake for his birthday and the police came screaming in in the vehicles and just told everyone to get back inside their factories,” he said.

– with ABC and AAP