The world's first confirmed case of a fire tornado has been documented by Canberra researchers, using evidence collected from the devastating 2003 Canberra bushfires.

Researchers have long speculated about the ability of a fire to produce a tornado, but until now they have not been able to scientifically prove it.

The study involved collecting a vast quantity of evidence from the Canberra bushfires and has been published in the scientific journal Natural Hazards.

Lead researcher Rick McRae says the fire tornado formed in the ranges west of Canberra before pushing into the city's suburbs.

"The one that we looked at showed that as it approached the edge of Canberra, its basal diameter was nearly half a kilometre, and the damage indicates that the horizontal wind speeds around it were in excess of 250 kilometres per hour," he said.

"There is also a vertical wind in it at 150kph."

He says tornados are different to the whirls often associated with fires.

"The fire whirl is attached to the hot ground," he said.

"A fire tornado, like a true tornado, is attached to the underside of a thunderstorm."

Mr McRae says the study provides crucial information on fire behaviour.

"Our analysis indicates that the tornado had a rating of at least a two on the enhanced Fujita scale of tornado severity [scale of 0-5, with five being the worst]," he said.

"It had major effects on the behaviour of the fire on the urban edge and had enough force to remove roofs from houses and to blow cars off the road.

"It's given us an ability to recreate the behaviour of this thing and for the science community, document what a fire tornado may actually be."

Mr McRae says he hopes the case will help emergency authorities better understand the nature of bushfires.