Floral tributes have been laid outside a two-storey house in Gladstone, in central Queensland, that was "completely destroyed" by the blaze.
The victims have been publicly named as Jordana Johnson, 36, her 12-year-old son Jordan Norris and his friend Chazz Mather, also 12, although police are yet to formally identify the bodies.
A fourth person escaped the blaze and was treated for minor injuries in hospital, police confirmed on Thursday.
The blaze erupted in the early hours of Wednesday, reportedly during a sleepover, causing the house to partially collapse.
The community has rallied around the victims' families as police investigate the fire's cause, setting up a second crime scene at a nearby street.
Homicide detectives have arrived but police said they were keeping an open mind with the cause of the fire yet to be determined.
"It's three unexplained deaths," acting Detective Superintendent Luke Peachey told reporters.
"We're keeping a very open mind as to which direction this investigation takes.
"There are probably more questions than answers at the moment."
Heavy earthmoving equipment was set to remove the house's roof on Thursday as authorities looked to retrieve the bodies "respectfully".
"It's going to be a very challenging investigation," Det Supt Peachey said.
The fourth person who escaped the fire was known to the families and had spoken to police, he said.
The investigation has no person of interest to date.
More details also emerged about the morning of the fire, with police saying a number of people tried to help before the blaze engulfed the home.
"We don't hold anything against these people trying to help," Det Supt Peachey said.
"It was a hectic situation."
The Gladstone community has since been in mourning, with floral and online tributes flowing as locals try to comprehend the tragedy.
Representatives from a victims assistance program will doorknock the neighbourhood to ensure residents get the correct information about the investigation and avoid community unrest.
Police are also updating the victims' families, Det Supt Peachey said.
"The whole community of Gladstone is in shock," he said.
"We've seen a number of investigations we've had like this where there is people pointing fingers at others."
Gladstone state MP Glenn Butcher urged locals not to spread misinformation online.
"I kindly ask that we all respect their wishes and refrain from posting unwanted comments on various posts," he said.
"There is a lot of incorrect information circulating, and the focus should be on supporting those affected, not spreading misinformation."
Anyone who witnessed or has footage of suspicious activity in the Whiting Street area of Gladstone from 5am to 6.30am on Wednesday has been urged to contact police.
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