Senior Sergeant Jason McCoy, of Oamaru, said the AOS and uniformed officers were called to a property in Wansbeck St about 11am ''after a man was observed presenting what was believed to be a firearm in public.''
''He has been arrested without incident and is currently speaking with police,'' Snr Sgt McCoy said.
A witness who provided a photo to the Otago Daily Times said about 12 AOS members were involved in the operation at the house.
They shouted instructions at the occupants.
At least two were handcuffed and ordered to sit on the footpath outside the house.
A reporter earlier witnessed four police cars parked outside the property and officers were seen coming and going.
Tees St in Oamaru was also blocked to traffic for a time.
Police and a St John ambulance were also stationed near the corner of Wharfe and Arun Sts.
Police were letting people through the cordons as of 12.45pm.
A witness earlier reported six marked and unmarked police cars heading north through Hampden about 11.40am.
Another witness reported seeing police cars racing through Palmerston.
The police cars and at least one van were later seen pulling into the Oamaru police station about noon.
