"The floor on the upper level was unstable, it was very thin and had been damaged by the fire so we had to access it externally."
He said the owner was not inside at the time the fire started.
"He had gone up the road and forgotten he had left something on the stove. It's a timely reminder to keep looking while you're cooking."
It was initially feared that one person may have been inside the building when the fire broke out.
A police media spokeswoman confirmed that all people in the building were accounted for 25 minutes after the initial reports of the fire.
A witness who works along Riri St said she noticed smoke when she arrived for work at 7.30am.
She said the smoke wasn't very noticeable at first but when she came back out "there were huge plumes of grey smoke high up in the sky".
She said it appeared firefighters had worked quickly to get the fire under control.
She was unsure whether people would have been in the building at this time.
Another witness said there were large flames coming out of the top of the building and the smoke was "so high you could see it from the other side of town".