A fire that destroyed a major Tasmanian power station last week was accidental, the fire service says.

The Tungatinah Power Station, located in the Central Highlands, was completely gutted during a fire last week.

The Tasmania Fire Service said fire scene investigations had been completed, though the investigation will continue for a several months.

"Following extensive scene examinations, fire investigators have determined the fire was accidental," Tasmania Fire Service Deputy Chief Officer Matt Lowe said.

"The preliminary investigation findings have identified several potential ignition sources which will be subject to further investigation over the coming weeks and months, however the fire has originated on the assembly bay floor, away from the main turbines.

"The investigation process so far has been complex due to the size of the facility, the significant structural damage sustained during the fire, and severe weather conditions experienced in the area last week."

Mr Lowe said fire investigators had worked closely with Hydro Tasmania, Tasmania Police and other agencies throughout the scene examination process.

"While ongoing assessment and recovery works will continue at the site in the coming days, the scene was handed back to Hydro Tasmania yesterday," he said.

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