Breathing apparatus was required by all attending firefighters, Mr Pearson said.
The fire was believed to have started in the kitchen-service area at the back of the 1970s building, which was renovated prior to opening as 88 Asian Fusion in November 2013.
Co-owner Adam Haugh said it appeared that the building had suffered substantial smoke, water, and some structural damage which would keep the restaurant closed for some time.
"It's going to require structural rebuilding, replacement of ceilings ... it's going to require a wee bit of work," Mr Haugh said.
He understood a formal fire investigation would be undertaken in the next few days.
"It's sitting there but we'll have it back to life next summer, hopefully."
- Greymouth Star