THE investigation into the fire that destroyed the Spotted Dog and the Federal Backpackers last month has concluded.

Queensland Fire and Emergency Services Area Commander John Pappas said investigators had confirmed the fire started in the kitchen of the Spotted Dog.

"Our fire investigation team have been making investigations and that has concluded," he said.

Mr Pappas said the cause of the blaze would never be known, however, "due to the nature of the fire".

The fire is known to have started in the Spotted Dog kitchen before travelling laterally through the roof of the building and nextdoor to the Federal Backpackers.

Mr Pappas said kitchen fires could be complicated with fittings such as cold rooms affecting the way a fire could burn.

A total of 62 people were evacuated out of the Federal Backpackers on the night of July 20 as the blaze burned into the morning of July 21.

It was a positive outcome considering the disaster coincided with the 20th anniversary of the Childers backpacker fire.

"There was quite a bit happening, it was quite concerning. All people were accounted for early on," Mr Pappas said at the time.

It was the first major fire in the city's CBD since the Church Pharmacy went down in flames in 2016.

Mr Pappas said the properties had been handed back to the owners and insurers.