Four fire trucks and several specialist units battled a blaze at a scrap metal yard in Lower Hutt suburb of Petone that caused a road closure.
More than 60 trucks were at the scene when a fire started before 6.45am in a machine cutting fridges before spreading to insulation materials, a Fire and Emergency spokesperson told 1 NEWS.
Parkside Road has been closed with the blaze also causing nearby businesses to be evacuated as a precaution.
Police are warning motorists to avoid Seaview Road with significant delays in the area.
One employee suffered minor smoke inhalation but did not require hospital treatment.
There is a possibility crews may be at the scene overnight.