Australia's largest union has accused the Victorian government of rushing the reconstruction of its failed tourist attraction, the Southern Star Observation Wheel, which mysteriously spun on its own overnight.

A WorkSafe inspector's report obtained by The Age says a five to six-metre-per-second gust of wind hit the giant wheel at 11.10pm last night, when it "broke free from its fixings and spun free for a period of time".

It has been reported that the wheel subsequently performed six uncontrolled rotations.

There are conflicting reports about what caused the wheel to turn.

WorkSafe today said it was understood slings attached to temporary holding points on the wheel somehow detacheded, allowing the wheel to turn uncontrollably.