Neighbours have reported smelling fuel as an explosion and fire tore through a Brisbane home early on Tuesday, killing three people.
A cry for help was also heard as flames engulfed the Everton Hills home, where a woman lived with her adult son.
Firefighters found the bodies of two women and a man in the blackened shell of the two-storey brick property, and police are trying to establish if the woman and her son are among the dead.
The house is now a crime scene.
"There are suspicious circumstances around this fire," Queensland Fire and Emergency Services Superintendent Bevan Moore has told The Courier-Mail.
"Calls from neighbours have indicated there were unusual noises associated with the fire ... there were explosions reported by neighbours, the smell of fuel, things like that."
Investigators don't yet know if the explosion sparked the fire, or if it was the other way around.
That will be a key question for forensic crews tasked with finding out exactly what happened at the Pavonia Street property about 5.30am.
Neighbours have described hearing a cry for help, and witnessing an extremely intense fire that forced the evacuation of some surrounding properties.
One resident heard a shout for help, before rushing outside and seeing flames tearing through the home.
"We heard a shout - help! - and my wife said 'Oh, the house (is) on fire just at the back'," the man, who did not want to be named.
"We were obviously very concerned about our property, but obviously for the neighbour as well."
Police Inspector Daniel Bragg said neighbours had reported hearing "a loud explosion, quite significant" and seeing flames that were visible from some distance away.
"We're investigating it as a suspect house fire until evidence comes to light that shows us otherwise," he told reporters.
"We're trying to put together the pieces of this jigsaw, what started this fire. We need to find out if it's suspicious, I mean, it might have been just a terrible accident."
Insp Bragg said it was extraordinary that no neighbouring properties were damaged, given the size and intensity of the fire.
"This is just an awful thing for the whole community."