A discarded cigarette started a blaze which destroyed a One Nation campaign truck in Hobart, discrediting claims by the party that the "left" was to blame.

Senate candidate Adam Lambert had been driving the truck, emblazoned with the faces of Pauline Hanson and her team, and was inside a Howrah shop on Sunday when the fire began.

On Thursday, police said the fire was not deliberately lit and firefighters revealed the likely cause was an ember from a discarded cigarette.

A One Nation campaign truck in Hobart caught fire. (One Nation/Twitter)

"This determination is based on there being no evidence of a deliberate ignition source, or any fault with the vehicle, in addition to CCTV footage not showing anyone at the back of the vehicle at the time," the Tasmania Fire Service said.

The white Holden ute caught fire at Shoreline Plaza the day after the federal election.

Mr Lambert posted a video to Facebook - showing flames leaping high above the cabin of the ute - saying he walked out of the shop to find the vehicle ablaze.

"If you don't like us don't vote for us, but for those magnificent supporters who have voted for us, this is a little more encouragement on how we have to work a bit harder for you guys next time," he said.

Senator Hanson said "someone was seen torching it before fleeing".

"It is amazing how the left call for tolerance but act like they're above the law when you don't agree with their ideologies," she wrote on social media.

While there is no evidence of a crime, police want to hear from anyone with more information about the fire.