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Southern Region fire safety officer Stuart Ide told the Otago Daily Times the cooker, understood to be relatively new, was portable and about half the size of an oven.
A neighbour of the Glasgow St property notified the Fire Service at 5.50am on September 17 after being woken by the sound of the fire, which caused the top floor of the two-storeyed home to explode.
Mr Ide said the exterior of the upper floor of the home, containing the kitchen and living area, was made from Polite board.
''Once it gets heated, it explodes and goes off like rifle shots,'' Mr Ide said.
Through his investigation, Mr Ide discovered the cooker had been left on a low setting for about eight weeks.
He was unable to ascertain what had caught fire, but it was possible the cooker eventually overheated.
''The thermostat is clicking on and off all the time. It's possible that overheated itself, then the element would just go on fire.''
Mr Ide said he ''fully believed'' the cooker was left on accidentally and it was possible it was knocked while the area was being cleaned.