Milton police were initially called to a Narrowdale Rd residence near Milburn at 3pm when a 57-year-old man threatened to commit suicide.
Sergeant Martin Bull, of Balclutha police, said a police officer tried to calm the man, but he pushed the officer to the ground and threatened him with a nail gun.
"He would not be spoken to. So the officers backed away and left the address."
With assistance from Milton, Balclutha and Lawrence police, they cordoned off the area and waited for armed offenders squad to arrive.
Traffic on State Highway 1 was diverted either side of Narrowdale Rd at Milburn for about two hours.
Sgt Bull praised the man's neighbour who sat with him, trying to keep him calm until the armed offenders squad arrived.
The 57-year-old was unco-operative and had to be pepper-sprayed before he could be apprehended.
Sgt Bull said the man was at Milton police station last night awaiting psychiatric assessment and was likely to be charged with assaulting a police officer and threatening to cause grievous bodily harm.
