A police operation that evacuated the Sydney Opera House was sparked by "information on social media".
Police ran operations at the Opera House and in the beachside suburb of Manly on Thursday, but did not provide details on the nature of the threat.
Helicopter shots showed the usually crowded hub completely deserted and afternoon concerts were cancelled.
Police issued a release at 15:30 AEST (04:30GMT) saying that both operations had concluded.
The operation resulted in the cancellation of one ferry service between Manly and Circular Quay.