The fire began shortly before 9am on Saturday after a man turned an electric heater on and then left it to do something in another room, Mr Ide said.
"When he came back down he only just managed to get out [of the house]," Mr Ide said.
A flash of fire had chased the man down a hallway but he and his dog managed to escape unharmed.
The man then warned the two people in a flat above and called the fire brigade.
"They were all waiting on the driveway when we arrived," Mr Ide said.
Several people living around Fernhill Rd had also called the fire service.
Mr Ide said by the time the three fire appliances arrived at the Fernhill Rd address the bottom flat was "well underway" and the lounge area of the top flat was also alight.
"It was made more challenging because it was a body corporate situation where the fire started in a flat on the ground floor and then spread to the one above it," he said.
While fire crews had the fire under control "within five to 10 minutes" of arriving, the three fire engines stayed for another four hours dampening hot spots and making sure the fire was completely out.
The bottom flat was "extensively damaged" but the fire was contained to the lounge area of the top flat.
But there could have been less damage if smoke alarms had been installed, Mr Ide told the Otago Daily Times.
Mr Ide said having a working smoke alarm in the bottom house would have increased the occupant's reaction time and the fire service would have been called sooner.
"There were no smoke alarms in the house," he said.
"All houses should have them - they are your last line of defence."
The fire service recommends an average three bedroomed house should have five alarms fitted throughout.
