Mechanical friction is believed to have caused a fire at a Kooragang Island fertiliser plant on Sunday.
Numerous investigations are underway into the cause of the blaze that broke out at the Egret Street plant just after midday.
Wengfu Australia chief executive Damien Heath said a quantity of sulphur bentonite was being screened at a facility operated by Port Hunter Commodities.
It is believed the screening equipment ignited the bentonite when it was moved at the conclusion of the screening process.
"It seems the tracks moving on the floor have created some friction and ignited some sulphur dust that would have been caused during the screening process," Mr Heath said.
An initial attempt to smother the fire was unsuccessful.
About 60 firefighters from across Newcastle rushed to the facility following a triple-zero call.
A dozen workers were evacuated, while the adjacent Newcastle Coal Infrastructure Group plant was forced to cease operations.
Crews remained on the scene as a precaution for several hours after the fire had been extinguished.
No one was injured and no property was damaged by the fire.
"Usually this product would not be handled at this facility, it would be kept up the road at our other facility," Mr Heath said.
"We believe all of the safe work procedures were followed. That's why we need to conduct these investigations to find out how the fire started."
