Fire investigator Murray Milne-Maresca described the damage at the business, near Winton, as a "total loss".
A Fire and Emergency spokeswoman said crews from Nightcaps and Winton, and a tanker from Otautau were called to the fire in Heddon Bush at 1am this morning.
When crews arrived, they discovered a well-involved blaze at a building about 80 x 60 metres in size.
Crews at the scene transmitted a second alarm and another truck from Otautau showed up to assist, along with an additional tanker as well as an aerial appliance from Invercargill.
The blaze is being treated as suspicious and fire investigators were attending the scene this morning, the spokeswoman said.
Mr Milne-Maresca said the investigations were being held up "due to structure and stability".
"Investigations will definitely take a few days as we work with the insurers, owners and the police," he said.
