However, Police acknowledged they are making inquiries about the fire - including working to find a person thought to live at the house.
"Police are making inquiries to establish the whereabouts of an occupant who has not been located at this time," a statement said.
St John also confirmed they were called to a fire incident in Manurewa shortly after midnight.
Three ambulance vehicles and one clinical manager were sent to the scene.
"We assessed and treated one patient with serious injuries who was transported to Middlemore Hospital."
The house is now under Police scene guard until it can be determined to be safe to enter.
An investigation is ongoing, Police said.