The theft of a catalytic converter is being touted as a possible cause of the devastating Papakura scrap yard fire at Queen's Birthday weekend.
Fire and Emergency New Zealand refused to comment about the huge Papakura blaze, with a spokesman saying the investigation is ongoing.
But sources familiar with the investigation say a thief using a cordless grinder or similar device to remove a car's catalytic converter may have ignited a petrol tank.
The subsequent disastrous fire on June 6 devastated the car yard as it tore through hundreds of vehicles.
The fire broke out on a quiet Sunday afternoon.
After Herald inquiries, police this week confirmed converter thefts were rising in places, as thieves targeted the emission-cleaning devices for valuable metal parts.
An experienced New Zealand fire investigator said broadly speaking, a catalytic converter thief could cause a major fire if a grinder was misused.
"Misuse of a cutting device is certainly a potential ignition source."
There is no suggestion the Papakura car yard was at fault but the company directed queries to a lawyer, who has been approached for comment.
Police have also been approached for comment about the fire and the catalytic converter thief theory.
Cordless grinders, available new for less than $100, are thought to be a significant factor in the rising number of converter thefts.
Once underneath a car, thieves using these grinders and adding a zip blade or cutting disk can remove converters in well under a minute.
Police have confirmed dozens of catalytic converter thefts were reported in Canterbury alone in the past few months.
A Herald reader said he was concerned about people on Facebook pages who boasted of travelling from faraway towns to Christchurch to buy converters for as little as $150.
"Now if that's not an incentive to buy them, nothing is," he said.
New or replacement converters bought legitimately can cost well over $1000.
Some companies now sell security cages to protect converters from thieves.
Although converters vary by make and model, their use of metals including rhodium, platinum, iridium and palladium drive their allure to thieves.
Prices for the metals have soared in the past year.
Rhodium was up 166 per cent on this time last year, according to Yahoo! Finance, and is many times more valuable than gold.
Hybrid cars are more typically targeted, as they have a greater concentration of valuable metals than traditional petrol or diesel cars, the Sunday Times reported this week.
Multiple police departments in the United States and Britain have reported a surge in converter thefts in recent months.
In Colorado, the catalytic converter crime wave is so severe, a state-wide initiative to track the devices through serial numbers was being considered.
In Texas, an attempted theft in April led to gunfire when members of the public in Houston interrupted thieves.