New South Wales Police say they conducted an operation at Sydney Opera House and at Manly this afternoon as a "precautionary measure".

Officers had carried out searches in response to information on social media, but nothing was found.

The area leading to the Opera House steps was cordoned off with railings for more than two hours and people were told to leave the area.

That barrier has now been removed and the Opera House foreground reopened to the public.

The Manly ferry service is operating as normal after the cancellation of the 1:20pm service. A second ferry was also delayed.

"Following information on social media, police conducted an operation in the vicinity of the Opera House and Manly as a precautionary measure," said police in a statement.

"That police operation has now concluded."

Police have not confirmed if the two operations were linked.