Fire and Emergency NZ incident controller Steven Callagher said several large buildings were damaged in the fire and a lot of toxic substances were released as a result, due to the presence of lithium iron batteries at the facility.
He said while the cause of the fire was yet to be confirmed, initial information suggests it could have been caused by lithium batteries.
Callagher said the structure was currently very unstable, and too unsafe for fire investigators to enter.
He said he expected the remaining crews - about 20 - to be on the scene throughout today to dampen down hotspots, and they would also be bringing in diggers to demolish the building to make it safer.
Callagher said he was aware one of the Auckland aerial appliances broke down last night during the firefighting.
Meanwhile, shift commander Karen Larking said the warning for people to keep their windows closed had lifted - although some local roads remain closed due to concerns with visibility.
Yesterday, assistant commander Barry Thomas said the incident had been scaled down to a "second alarm" and fire crews were working to extinguish hot spots using ladder trucks.
"There is significantly less smoke, but it continues to affect communities in Glenfield and Witheford Heights," he said.
"We advise people to stay inside and to keep windows closed if they smell or see smoke."
