Thick smoke blanketed much of Northern Tasmania yesterday after an arsonist went on a rampage in Victoria.
The arsonist lit test fires before starting the blaze that spread into a Victorian coalmine.
Victorian Chief Commissioner Ken Lay said police believe the same person or people lit a test fire in Hazelwood on January 28 to see how the fire would act before setting another in the same area on the morning of Sunday, February 9.
Lead investigator Inspector Mark Langham said the three fires were set over a three- kilometre section of the highway, two in grassland and paddocks and the other in a pine plantation on two sides of a dirt track.
"The three fire seats that were set along the Strzelecki were systematically set to cause a large bushfire," he said.
The person responsible was likely to be someone who lives or works in the Latrobe Valley or wider Gippsland region, with the fires lit along dirt tracks leading into plantations behind the highway that also provided easy getaway routes.
Police had saturated the area with extra patrols but the firebug still managed to set the fires.
The deliberately lit blaze was one of two fires that spotted into the Hazelwood mine, with a fire that began on February 7 also moving through the Yallourn coalmine and Australian Paper Maryvale mill complex.
Both seriously threatened the western side of the town of Morwell, Mr Lapsley said.
The ongoing fire is burning over three kilometres in worked-out faces of the Hazelwood mine.
Mr Lapsley said the fire would take at least another fortnight to put out.
There are no suspects at this stage.
The Tasmania Fire Service put the North on alert yesterday saying smoke and ash crossing from the mainland would be visible.Conditions are expected to ease today.