A microwaveable wheat bag was the cause of a house fire that killed a 90-year-old woman in Hobart on Wednesday, firefighters say.

The home on Springfield Avenue in West Moonah was fully engulfed when crews arrived about 2.30pm.

The woman's body was found inside.

Fire investigators today concluded the fire was accidentally started by a wheat-filled head pack which overheated in the microwave.

"I'll miss her": Phyllis Ward had known her neighbour for 20 years. ( ABC News )

"Our thoughts are with the loved ones of the person who died," the Tasmania Fire Service said in a statement.

Phyllis Ward, a neighbour and long-term friend of the 90-year-old, said the woman was a selfless and community-minded person.

"You couldn't wish for a better friend, she'd do anything for you," she said.

"I'm very sad, I was only talking to her on Sunday night, she rings me practically every night or every second night because she's concerned about me and I was always concerned about her.

"She's a good neighbour, I'll miss her, no doubt about that."

In 2017, a New South Wales coroner called for an awareness campaign about the dangers of wheat-filled heat packs after an elderly woman died in similar circumstances.

It's the second fatal fire in Tasmania in the past week.

A 61-year-old man died in a shed fire at Swansea on Friday.