A Fire and Emergency New Zealand (Fenz) spokesman said they received reports of a building on fire at 7.57am and initially responded with two fire trucks from Invercargill and Kingswell and a tanker from Wallacetown Volunteer Fire brigade.
"We arrived at the scene to an ablaze building fire, then escalated to what we call a second alarm."
Four fire trucks, three tankers and two support vehicles were then sent to the scene.
"Multiple crews are using multiple hose lines and working to extinguish the fire.
"At this stage, the cause of the fire is unknown."
A spokesman from Hato Hone St John said they responded to the incident with one ambulance, one rapid response unit and an operations manager.
"Our ambulance officers have treated and transported one patient to Southland Hospital in a critical condition," the spokesman said.
A fire inspector will attend the scene to assess the causes of the blaze.
