Mr Newman said it appeared some sort of fuel was used to light the fire, but it was too early to tell what type of accelerant had been used.
"There was quite extensive damage around the front area of the building, and obviously the fire has got up into the ceiling, the roof area, which has caused damage in the ceiling cavity as well.''
Asked whether the fire could be linked to a disgruntled Winz customer, Mr Newman said he did not want to speculate, but added: "We will be looking at a number of avenues of inquiry, that being one of them.''
Police were talking to a man who was assisting with inquiries.
Mr Newman said it was too early to tell whether charges would follow.
Police are encouraging anyone who saw anyone on foot in the Mountwell Cres area between 2.30am and 4am today to contact Glen Innes police on (09) 524 1921.