Chief Inspector Kieran Baggoley said the two bodies were found by fire crews after the fire was extinguished at the suburban Edwardstown property early on Monday.
They were believed to be related, with media reports they were a mother and daughter and that the incident involved a possible murder-suicide.
Neighbours told investigators only two people lived at the house with early inquiries involving major crime and forensic officers.
"It's important for us when we go to scenes like this that we have that level of response," Insp Baggoley told reporters at the scene.
"We want to make sure we've covered all bases as to what could have occurred.
"We are not ruling out anyone else being involved. However, we are focused solely, at this stage, on the two occupants."
Fire crews were called to the home at about 5 am after a neighbour noticed the blaze.
By the time they arrived, one room was engulfed in flames and the rest of the property was impacted by heavy smoke.
Damage was put at $100,000 with the fire limited to one room which Insp Baggoley said appeared to be used as a spare room.
It was believed the two women had lived at the property for more than two year and were not previously known to police.
Post-mortem examinations will be conducted which Insp Baggoley said would be critical to understanding what happened.
"Any time two persons are located in an address and they're deceased, that is a tragedy," he said.
"There's no sugarcoating that. That's why we have all the resources here to investigate it."
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