A fire service spokesperson has said the fire in a dairy factory tower near Pukekohe has been put out.
The fire broke out this evening in a drying tower for milk products at the plant at Paerata owned by New Image Group.
A fire officer at the scene told ONE News the fire will be burning for some time as it is very difficult to put out.
"There's a milk powder drying vat inside a building that has caught fire and it's a little bit awkward getting access in to put the fire out," said Craig Monrad, Counties Manukau assistant area commander.
"We have set up covering deliveries and applied some cooling water until we can get into the seat of the fire," he said.
Bystanders at the scene say smoke was pouring out of the tower.
One man said he drove past the scene just after 5pm.
"There was no one here and just thick smoke pouring out of the building on the upper floor," he told ONE News.
At least 20 fire appliances turned out and firefighters worked to ensure surrounding buildings are not threatened by the fire.
There are no reports of any people affected.