The rental house had smoke alarms but they had no batteries in them, and the back door was permanently locked, leaving the house with only one exit, Mr Wilson said.
He said a woman and a baby had been able to get out the front door, but when the woman tried to go back in to help other family members she was forced back by the heat. Four other occupants of the house had got out through a window.
Mr Wilson said the initial call to the Fire Service had indicated there were people unaccounted for.
"However, when we arrived everyone had got out safely but the house was well involved," he said.
One of the occupants had rescued two dogs and firefighters had rescued a rabbit from the property.
Mr Wilson said if there had been working smoke alarms in the house, the family would have had early warning of the fire. "Then they could have closed the bedroom door to help contain the fire and got out quickly."
He said it was "very concerning" that an external door could not be used, and that young children were able to get hold of matches.
Part of Bamber St was cordoned off while emergency services worked to help the occupants and get the fire under control.
Neighbours told the Wanganui Chronicle they knew nothing of the fire until they heard sirens and smelled smoke. They said the family consisted of a couple and four young children, who had moved to the street about two months ago.