Several officers swarmed on the Kakanui Store, which also houses a liquor outlet, in High St about 2.55pm after it was reported a man entered the premises brandishing what was believed to have been a firearm.
Three police cars and several officers were still at the scene about 5pm, conducting interviews and carrying out a scene examination when the Otago Daily Times arrived.
Detective Sergeant Hannah Booth, of Oamaru, said the man who entered the premises and threatened staff was wearing what was described as a dark jacket and his face was disguised by black cloth and sunglasses.
She said the store's owners had been left shaken by the incident, but were unharmed.
''Understandably they are shaken up, but they're assisting police at the moment.''
The investigation was in its early stages and it was ''unknown'' exactly what, if anything, had been taken until a scene examination had been completed, she said.
''We're just speaking with witnesses and members of the public at this stage.''
Det Sgt Booth confirmed two teams of dog handlers from Dunedin attended the scene in an unsuccessful effort to track down the offender.
Oamaru police (03) 433-1400, Crimestoppers 0800555-111.
