About 70 diners and 30 staff were evacuated when fire started within an extraction system from the kitchen of Botswana Butchery, on Marine Pde, at about 6.30pm.
No-one was injured.
Good Group chief executive Russell Gray said the group was removing stock from the eatery and working through insurance assessments.
"The damage is pretty serious, in one corner of the restaurant, from the intake right through the upstairs bar and into the roof cavity.
"There's a lot of water and smoke damage and damage to furnishings and stock.
"We'll be under repair for a minimum of five weeks."
The popular restaurant, which opened in August 2008, had business interruption insurance, which would cover profit losses and renovation.
Decisions relative to staff would be made over the coming week, Mr Gray said.
The end of the winter season meant some temporary staff would be leaving in any case, while permanent staff would be looked after within the multiple bar and liquor store portfolio.
Fire inspector Mike Cahill, of Invercargill, said yesterday the fire started within the extraction system from the kitchen and ignited at roof level.
Mr Gray said he would be interested to see what the fire inspection report said once it was compiled, but he said the extraction unit was cleaned regularly.
The company was not assigning blame to anyone, he said.
