Police are treating last week's deadly caravan blast in north-west Queensland as a double murder-suicide.

The explosion in Mount Isa killed 38-year-old Charlie Hinder and his two children — four-year-old River and seven-year-old Nyobi.

Debris from the blast was found more than 50 metres away from the scene, forcing at least 55 nearby households to evacuate.

Investigators now believe explosives were used as an ignition point for the blast rather than gas bottles located at the scene.

River, Charlie and Nyobi Hinder died in the explosion. ( North West Star )

Police are now treating the deaths of Nyobi and River as suspicious and the death of their father as non-suspicious.

They believe no-one else was involved in the matter.

Mount Isa District Officer Superintendent Russell Miller said the next step was to determine what caused the explosion.

"We haven't been able to identify that at this stage but certainly, at this point in time, we're looking at some sort of explosive device or equipment that has caused it," he said.

"It has occurred inside the caravan. The explosion has occurred inside the caravan, not outside.

"We're still obviously waiting on a lot of results coming back from our forensic testing and scientific testing."

He said police were also still trying to establish a motive.

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"I mean who could come [up] with a reason for those sorts of actions."

He confirmed police were looking at Charlie Hinder's Facebook page, which reportedly featured a goodbye letter from the father.

"Our investigations have been quite extensive to date so everything that we have gleaned from social media, our forensic and scientific testing was all part of our current investigation," he said.

Superintendent Miller said the explosion had devastated the local community.

"This was a horrific event which has had a significant impact not only on the families, neighbours and friends of the victims, but also the wider Mount Isa community," he said.

"At this time we appeal to the community to respect the privacy of the immediate and extended members of the Hinder families while they come to terms with this tragedy."

Mt Isa Mayor Tony McGrady said government agencies held a public forum earlier this week to offer advice and support to community members who were still in shock.

He said confirmation the tragedy was a murder-suicide wouldn't "come as a great surprise to some people".

"I just think they've accepted the fact now that police have made a formal announcement, I suspect there'll be further announcements in the not too distant future," he said.

Superintendent Miller said investigators would continue to work closely with the state's northern coroner on the matter.

Police have previously said it could take weeks, if not months, to fully complete the investigation.