Multiple fire crews attended the blaze, which collapsed the roof of the Rowella Road property and gutted much of the interior. Tasmania Fire Service estimated the total loss at $300,000.

Tasmanian Police Constable Alex Long, who attended the scene, said the occupants were transported by ambulance to Launceston General Hospital as a precaution as their injuries were not believed to be serious.

Fire crews from Kelso, Beaconsfield and Gravelly Beach attended the blaze about 8.15am after being alerted by neighbours.

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But it was a twist of fate that led Nick Campbell to lend a hand.

"We were delivering concrete to a job at Rowella," explained Mr Campbell, owner of BINC Premix Concrete. He was the last in a chain of six or seven trucks bound for the job from Western Junction at intervals of 15 minutes.

Travelling north on the East Tamar Highway, Mr Campbell missed the Batman Bridge turnoff and lost about 10 minutes redirecting. On passing the home, he noticed smoke over the vegetation at its front from the high vantage point of his truck.

"That smoke's not coming out of that chimney, it's coming out of the roof cavity," he said.

Mr Campbell then pulled over to check the house, ensured neighbours were calling Triple Zero, and knocked on the front door - to no answer. On checking the back of home he met the man, who was unaware of the fire.

With a neighbour grabbing bags, Mr Campbell said he helped the woman out of the home in her wheelchair and ensured both were okay before getting back to his vehicle.

"I was a bit worried because I had a fully loaded concrete truck out the front," he said. "Under the circumstance that really wasn't as important."

"You don't really expect to see that stuff on your way to work.

"[But] you do what you've got to do, don't you."

Constable Long noted the early action helped the elderly couple leave the house before they could suffer smoke inhalation.

Rowella Road was closed for a number of hours from the Batman Highway to just after the intersection with Hudson Street. Investigations into the cause of the fire were still being finalised Friday afternoon.

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