The underground truck fire at Newmont Waihi Gold which left 28 miners trapped in refuge chambers was caused by a split pipe.
The Ministry of Business Innovation and Employment, formerly the Department of Labour, have completed its investigation into the underground truck fire, which happened on July 17.
As a result, 28 miners were trapped in three refuge chambers for up to seven hours.
Newmont's external affairs coordinator Kit Wilson said results of investigation concluded the mechanical failure was caused by a split hydraulic pipe, which sprayed oil on to the engine exhaust.
"The oil ignited and caused a flashback to the source of the oil, which then caught on fire."
"The truck is a standard hydraulic truck, no different from what you'd see at a building site or a subdivision construction. It's not a specialised underground mine truck," he said.
The truck was about 100m underground, on the main line when it caught alight about 5am. Mr Wilson said it had since been moved to another area of the site.
Photographs of the truck have been taken but have not been released to the public, as they formed part of the investigation.
Newmont Waihi Gold general manager Glen Grindlay earlier said the front tyres were destroyed but the back four were still inflated and could still cause a problem if they exploded.
Newmont Waihi Gold have almost completed its investigation into the incident.
Mr Wilson said preliminary findings showed the company needed to make some changes, particularly to update staff emergency contact details.
A spokesperson from the Engineering, Print and Manufacturing Union (EPMU) said the union would go through the investigation report with a fine-toothed comb. "Twenty-eight people were in a lot of potential danger so when we see [the report], we'll ... see if any lessons can be learnt for the future."