The cause of a massive fire at a Ngongotahā car wreckers yard which saw hundreds of cars go up in flames last week has been revealed.

Fire investigator Lynda McHugh confirmed the fire at Direct Auto Dismantlers on Taui St started when a car was crushed with a battery in the boot.

She said it was "definitely" a battery and not an LPG cylinder as this would have caused a loud bang, which it did not.

She said the fire was not being treated as suspicious. Witness accounts had helped with the investigation, but anyone who was in the area between 6.30pm and 7pm last Tuesday was urged to contact the Central Fire Station.


McHugh said while the buildings were insured, the vehicles were not.

Fire crews arrived to find a "well-developed fire" at the car wreckers last Tuesday around 7.10pm . Within an hour, the fire had been upgraded to a fifth-alarm and 22 crews from across the region were at the scene.

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Smoke was billowing from the lot and could be seen as far away as the Mangorewa Gorge.

Fire and Emergency New Zealand incident controller Hamish Smith said the burning cars, equipped with combusting linings, seats, tyres and even oil, continued to light up at pace and the scene was "unpredictable" and hazardous, Smith said.

Not only that, but two large buildings filled with sawdust and dry timber bordered the blaze.

"There were a lot of potential risks," Smith said.

A firefighter on the scene said if it had caught one of the buildings, they could have been dealing with a catastrophic airborne fire.