Peter Williams, the father of the man responsible for shooting another at a business in Sydney's south-west yesterday, has been released on bail after he was charged with discharging a firearm.

Mr Williams, 52, was arrested at the sign-making business, after son Wayne Williams, 33, shot three brothers – one fatally – over what is believed to have been an alleged business dispute.

Wayne Williams reportedly ambushed the three siblings upon their entering the shop, firing upon them with a semi-automatic rifle and forcing them to take cover in the adjacent factory.

Emergency services rushed to an industrial estate on Heald Road in Ingleburn at about 10.45am yesterday following reports of a shooting.

Mick Bassal was shot dead. (Facebook)

The body of Mick Bassal was found at the scene and his brothers Terry and Mark were taken to Liverpool Hospital with gunshot wounds.

Gunman Wayne Williams then holed himself inside the Inline National Signage building for more than six hours as heavily armed officers and police negotiators locked down the area.

At around 5pm Mr Williams took his own life.

The family released a statement today which said the brothers had contracted Inline Signs but the work had not yet been completed.

"Michael, Terry and Mark Bassal were involved together in a construction business," the statement read.

"We are instructed that their connection to the alleged gunman and those subsequently charged was solely related to that construction business.

"We understand that the proprietor of that business, being one of the persons now charged, requested a meeting at the signage factory.

Special Operations police surrounded the building as Williams locked himself inside. (9NEWS)

Police created a one kilometre exclusion zone. (9NEWS)

"That meeting was organised after a number of requests as to the status of the signage, and then for a return of money already paid.

"We understand that, as they arrived at the premises, they were immediately shot at and Michael Bassal died almost instantaneously.

The industrial area. (9NEWS)

The shooting took place inside a signage factory. (9NEWS)

"We are nevertheless instructed to stress that this incident arose solely from dealings between the two businesses."

The 30-year-old owner and partner of Wayne Williams, Chantelle Tonna, has since been charged with conceal serious indictable offence and was granted strict conditional bail.

A crime scene has been established at the factory and police are set to continue their investigation.