Emergency services were called to the Springfield Lakes property, west of Brisbane, about 8pm on Friday after reports the woman had collapsed.
When responders arrived, they found the 23-year-old woman unconscious and not breathing. Her two young children were at home at the time.
She died at the scene.
Detective Inspector Michael Manago said the woman's husband, 26, and his brother, 28, who both lived at the property, were speaking with officers.
He said the children were being cared for off site.
The family were originally from Afghanistan and had only recently moved into the property, police said.
"Detectives are running out a number of lines of inquiry in regards to what occurred overnight," Det Insp Manago told reporters on Saturday.
"I would like to say this is a terribly tragic event, especially given young children being in the home, and our thoughts go out to the victims, family and friends who are naturally impacted by what's transpired."
Forensic officers were still combing through the property more than 16 hours after the emergency call.
Police tape was placed around the home, while several investigators were focusing their attention on an outdoor area of the residence.
A Mercedes-Benz was also seized.
Police did not reveal what, if any, injuries were visible on the woman or how she was believed to have died.
The scene was nonetheless described as confronting for the paramedics and police who first attended the home.
"As you can imagine, any scene such as that, is quite a chaotic scene," Det Insp Manago said.
"They acted professionally and I just want to acknowledge the great work they did in attempting to revive that young victim," he said.
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