Emergency services rushed to Bayside Court in the small coastal community of Thorneside on Sunday morning to find the townhouse ablaze.
Up to 30 firefighters worked to extinguish the flames which were so intense they caused part of the roof to collapse.
Neighbours rushed to help and tried to get people out but Detective Inspector Paul Dalton said it was a "futile effort".
An eight-year-old girl was found dead inside the home.
Det Insp Dalton said a 31-year-old woman who was babysitting remains unaccounted for as police are unable to get full access to the destroyed home.
"We hold grave concerns for her welfare," he told reporters on Monday.
Emergency crews are working to stabilise the structure to ensure it's safe to access the home. (Savannah Meacham/AAP PHOTOS)
A third person, who was a family friend living in the garage, was treated for smoke inhalation and taken to hospital in a stable condition.
The parents of the girl were interstate at the time of the blaze and have since been informed of the tragedy.
"They are obviously devastated. They've been offered support by police and they will continue to go through that," Det Insp Dalton said.
It remains "undetermined" whether the blaze is suspicious until officers can enter the home and identify the cause.
"There's nothing to say that this fire is suspicious in any way, but we will treat it as though it is until we make a determination one way or another," he said.
Tributes have been laid for the eight-year-old girl who perished in the blaze. (Savannah Meacham/AAP PHOTOS)
Emergency services remained at the scene on Monday to try and stabilise the home so police investigators can go inside.
"We've had structural collapse, so we have a technical rescue crew unit and aerial crew working now to stabilise the upper level, remove roof tiles so we can start the investigation," Queensland Fire Department Acting Superintendent Marck Burchard said.
Any neighbours who witnessed the tragedy are urged to reach out for help.
"These sorts of incidents even for seasoned police, fires and ambos are traumatic," Det Insp Dalton said.
"I can only imagine what it's like for someone who's not exposed to that normally."
Tributes have been laid near the home for the girl.
"Fly high beautiful girl," one card read.
The girl's great-aunt has set up a GoFundMe to help the family after the "terrible tragedy".
Redlands City Council Mayor Jos Mitchell said it was a "deeply upsetting" incident for the community.
"It is important during difficult times that we pull together in support," she said.
Local MP Don Brown said his thoughts are will the family and community.
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