A colonial-era statue honouring a former Australian premier who mutilated the body of an Aboriginal man has been toppled by vandals ahead of its planned removal.

In a ruling on Wednesday, a tribunal upheld a landmark decision to have the monument to William Crowther in Tasmania taken down permanently - putting to rest years of debate.

But in the hours before the ruling protesters cut down the structure by sawing through its legs.

The plinth was then left graffitied with the words “what goes around” and “decolonize”.

Crowther is accused of cutting off and stealing the skull of William Lanne, an Aboriginal Tasmanian leader known as “King Billy”, whose body was dismembered and used for scientific research after his death in 1869.