Crews responded to an alarm activation at an industrial building in Matheson Rd, Kennington, about 8.05am yesterday, a Fenz spokesman said.
A tanker and an appliance from the Invercargill station were initially dispatched, along with an appliance from Kingswell, the spokesman said.
While crews were on their way, a 111 call was received confirming there was a fire.
Two further appliances and a command unit from the Invercargill station and a tanker from Wallacetown were called.
The building contained fertiliser and a peat-drying area, the spokesman said.
The fire reached a size of about 50m by 50m and was located in the centre of the building, largely in its roof.
Crews remained at the scene through the afternoon, damping down hot spots and working slowly.
It was not clear yet what the cause of the fire may have been, but there was no indication it was suspicious, the spokesman said.
A fire investigator had been called.
A representative of BioActive Soils said the fire was confined to the other half of its building at the site, which did not belong to the company.
"At this point there are no injuries to BioActive Soil’s staff," the representative said.
