The boom came crashing down onto the construction site of a new university building in the early hours of this morning.
The crane driver managed to escape when a blaze broke out shortly before 9am and engulfed the diesel tank of the crane, more than 60m up in the air.
It was left to burn out because it could not be reached by firefighters.
But cables supporting the boom then seemed to snap bringing gasps from onlookers as it plunged and then smashed into a neighbouring building.
City worker Sean Nunan said: “The crane was really burning and then suddenly the boom just gave way – it dropped as though the cable had snapped or given way.”
A spokesperson from Lend Lease in Australia said no-one was injured.