When he saw the blaze he realised "my little fire extinguisher wasn't going to do much".
"All I could do is stand there and watch it burn."
Another of the first people on the scene said it was "horrible".
Kayla Korach was on her way to a work meeting at the Armitage Hotel when she saw the unit on fire across the road.
"I ran over to help straight away as I have trained with St John in first aid."
Ms Korach said an older woman who had come out of the house had collapsed due to shock.
She and another person helped her up and got her a chair and a blanket for the shock.
Ms Korach said the woman was suffering from smoke inhalation and had a painful burn on her leg. They gave her water and ice to ease the pain. The woman had since been taken to hospital by ambulance.
Ms Korach understood the woman had been cooking dinner when the fire started, but was not sure where or how the fire started.
The old wooden house "just looked orange" as the flames engulfed it, she said.
Firefighters had put out the flames and the scene was "smoky and dark".
Other witnesses have said the woman was confused and disorientated and had to be stopped from trying to get back into the burning building.
Senior Station Officer Len Sabin said firefighters expected to remain at the scene until about 9pm. A scene guard would be posted overnight.
He said the residents of the adjacent undamaged units had been asked to vacate for the night as the power was out.
He confirmed the female occupant of the front unit had been taken to hospital to be treated for smoke inhalation and minor burns.
Firefighters were working to determine the cause of the blaze.
Three fire appliances attended, two from Tauranga and one from Mount Maunganui.
