He was taken to hospital suffering from severe but not life-threatening injuries to his head, face and ribs.
A fire was then allegedly started by the group inside the warehouse and eight men were arrested by tactical police.
A further three men were arrested when they arrived at the property in another vehicle.
Footage of some arrests, seemingly captured by a witness and circulated online, shows the dramatic events unfolding at about 1pm.
Heavily armed officers can be seen detaining multiple men as more police vehicles, including an armoured truck, arrive.
Detective Superintendent Andrew Koutsoufis, robbery and serious crime squad commander, said the incident was exceptionally dangerous because of the violence used by the alleged offenders.
He said police inquiries were only in their infancy but investigators believe the alleged kidnapping was targeted and linked to organised crime.
At this stage it appears there are some organised crime and bikie-related links, he said.
One line of inquiry being examined by investigators is that the alleged kidnappers were seeking to secure a large payout in return for Mr Mancusos release.
One of the men arrested during the operation was armed with a gun.
Mr Mancusos father allegedly assaulted at Bringelly sustained minor injuries and was treated by NSW Ambulance paramedics.
Fire and Rescue NSW extinguished the blaze in Revesby about 2pm and handed the scene over to police.
Four of the 11 men were taken to hospital for treatment of minor injuries.
The rest were taken to Liverpool and Bankstown Police Stations and charges are expected to be laid.
Detective Superintendent Koutsoufis said it was too early to say what the charges would be.
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