The former Drifters Cafe building was found alight shortly after 11.30pm. Firefighters battled to contain the blaze over about six hours.
The old store, which is at least 80 years old, had been a popular cafe and performance venue for at least 20 years.
Granity is about 30km northwest of Westport.
Granity Volunteer Fire Brigade Station Officer Glen Standing said it had not been operating as a business lately but it was due to be handed over in a matter of days to a new owner who had intended reopening.
"There hasn't been a business in there for probably at least 18 months. The building was imminently going to be sold ... It was a matter of days. A lot of people are gutted.''
A small fire first reported at the rear of the building quickly took hold after the initial callout at 11.39pm.
"Because of the age of the building ... you look at something like that and know if it's going, it's going to go. It's a shame ... It's had a lot of history,'' Mr Standing said.
Two local firefighters living near the cafe noted a few flames to the rear of the building as they were driving to the nearby fire station.
However, a few minutes later when the brigade arrived the building was well alight.
About 20 volunteer firefighters, including the neighbouring Waimangaroa and Westport brigades, battled to contain the fire, successfully keeping it away from the neighbouring Torea Gallery in the old wooden post office building.
Mr Standing said about 80% of the Drifters building was seriously damaged and it looked to be a total loss.
An initial fire and police investigation said the cause was "undetermined''.
- Brendan McMahon
