Three Fire and Emergency New Zealand teams were alerted to the significant blaze off Mt Stuart Road, just after 9am.
At 10.15am, Fenz shift manager Jill Higgison said there were nine appliances at the scene, with roughly 30 firefighters. As of 11.30am the response had been scaled back and there were six appliances at the scene.
Two sheds that had been on fire were extinguished, while a third - 40m x 10m - remained burning.
Crews had contained the blaze and were "dousing the fire to make sure it doesn't spread" Ms Higgison said.
She said when the first crew arrived, from Waitahuna, they found a shed "well alight" and escalated to "third alarm".
She confirmed no livestock or people were inside the shed.
A fire investigator had been dispatched.
A police media spokeswoman said. Fenz have requested the police attend the scene, where there are multiple buildings on fire.
"Fenz were called at 8.59am and police were advised at 9.23am.
She confirmed the fire was taking place between on Mt Stuart Road between cross roads with Roberts Road and Burma Road in Johnston.
Pioneer Energy, which has a wind farm that runs along Mt Stuart Road, confirmed the fire was not at or near any of their assets.
