Police operations which forced the evacuation of the Sydney Opera House and Manly ferry wharf were launched after bomb threats were allegedly made against the Manly Ferry on social media.

The operations took place on Thursday from 2pm and NSW Police confirm 'information on social media' led to the large scale investigations near Sydney's city and the Northern Beaches.

'Following information on social media, police conducted an operation in the vicinity of the Opera House and Manly as a precautionary measure,' police confirmed after the operations concluded.

Threats were allegedly made to bomb the Manly ferry, according to Fairfax.

Ferries run between the two locations across the harbour, which are both densely populated tourist hot spots.

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The Opera House is pictured deserted after police launched their operation and cleared the site

The water police sit outside the Sydney Opera House while the police operation takes place on Thursday

Tourists still take the opportunity to take photos of the landmark despite the police operation behind them

From 5pm the Opera House had been reopened and performances and shows will continue as scheduled.

People were cleared away from the site by police, with barricades put up around the scene.

The 1.20pm ferry from Manly to Circular Quay was cancelled due to the operation, a Department of Transport spokeswoman said.

Barricades are put up outside the Opera House while another operation simultaneously takes place in Manly

People have reportedly been cleared away from the site by police, with barricades put up around the scene

NSW Police confirm a 'precautionary search' is taking place near the landmark at Circular Quay on Sydney's Harbour and another near the wharf at Manly on Sydney's northern beaches

Ferries run between the two locations across the harbour. Police have cleared people from the area and it's understood ferries have been cancelled