Emergency services were called to a rental car storage facility on Richard Pearse Drive in Mangere about 5am.
A section of the road has been closed, as dozens of fire crews work to bring the fire under control.
The Herald's Lynley Ward, is at the scene, and says thick black smoke is billowing from the building.
She says the smoke from a distance looks like a thick fog falling over Mangere mountain.
Firefighters are keeping watch on a fleet of rental camper vans parked next to the burning building.
