A New Zealand Fire Service spokeswoman said multiple calls were received about the blaze about 11.50pm.
The building, in Railway Tce, which some people called "the old store", was well alight when fire appliances arrived, the spokeswoman said.
Four pumps and four tankers from Gore, Clinton and Pukerau attended the fire.
A fire investigator and the police criminal investigation branch visited the scene on Saturday.
The inquiry into the suspicious fire was continuing yesterday, a police spokesman said.