Mr Smith said a police detective and New Zealand Fire Service investigator Stuart Law had examined the fire scene to establish a cause.
Detective Senior Sergeant Barry Bysouth said concerns the fire was suspicious dropped off almost immediately once the fire was out.
"It's effectively something that's more than likely caused by an accident which was more than likely hot ashes being left in a bucket."
Mr Bysouth commended the quick action of neighbours who had alerted emergency services.
"There was very good reporting by neighbours who called 111 immediately and their actions saved the house from burning down."
As well as calling firefighters, some neighbours made efforts to put the fire out with a hose, while another neighbour knocked on the door to check whether anyone was home.