Three family members who died in a house fire could have survived had they shut all the doors between them and the blaze, Fire and Emergency says.
Bhamini Theiventhiran, 39, her five-year-old son Bareth Theva Kaileshan and his 65 year-old grandmother Umadhevi Theiventhiran, died in the fire that took hold of the house in the Auckland suburb of Flat Bush in December 2016.
Firefighters found the trio huddled in an upstairs en suite bathroom.
Kaileshan Thanabalasingham, 47, who tried to escape the fire by jumping out a window, died in Middlemore Hospital a month later as a result of his injuries.
Two people who had been sleeping downstairs managed to get out of the house.
Fire and Emergency fire investigation national manager Peter Wilding said the fire was survivable.
By the time those sleeping upstairs discovered the fire, it had already blocked the stairs leading to the exit, he said.
The investigation found that two doors were left open between the top of the stairs and the area where the three family members were trying to take shelter.
"Tragically, our investigation shows that if they had closed the doors, the intense heat and toxic smoke from the fire probably wouldn't have reached them," Mr Wilding said.
Quickly escaping from a building that's on fire is usually the safest option, but that was not always possible, he said.
"If you're trapped inside, you can increase your chances of survival by shutting all doors between you and the fire, then placing bedding or clothing along the bottom of the door to keep the smoke out. This buys precious time for firefighters to arrive."
In her report into the deaths, Coroner Sarn Herdson said the exact cause of the fire could not be determined.
The fire started in the lounge, on the ground floor of the house, but it was not known what sparked it.
The remains of a single smoke alarm were found by fire investigators, and there was a significant lag time between the discovery of the fire and 111 being called - about 10 to 15 minutes.
The coroner reiterated the ongoing need to promote fire safety messages, including having more than one smoke alarm in a house.
Concerns were also raised about the use of polyurethane foam in furniture and recommended looking at ways to reduce furniture flammability.
Fire and Emergency said large, padded furniture containing polyurethane foam was the single biggest contributor to the speed fires developed.