POLICE descended on the Sydney Opera House following information posted on social media.

The operation started about 2pm with crowds told to leave the area as officers searched the landmark for an undisclosed object.

A simultaneous police operation was carried out at the ferry terminal.

A police op is currently underway in the #Sydney CBD & #Manly. As the operation is ongoing, no further info is available at this stage. — NSW Police (@nswpolice) January 14, 2016

A Transport Management Centre spokesman said one ferry service was cancelled and another was delayed but all others were running as normal.

“The 1.20pm Manly to Circular Ferry was cancelled due to a police operation and the 1.40pm Manly to Circular Quay ferry was delayed by 15 minutes,” the spokesman said.

Earlier a NSW Police spokesman said police were taking precautions after a threat was received about an object inside the Opera House.

“It’s a search for an object. There was a threat and we have to take it seriously,” the spokesman said.

He said the operation was still ongoing.

A Sydney Opera House employee posted an internal email to Reddit from the Head of Security, Emergency Planning & Response which said all performances and tours had been cancelled while employees were allowed to stay inside.

A police operation is underway at Sydney Opera House with people told to leave the area https://t.co/nFNSQpNWpA pic.twitter.com/QqY9LnWdfc — ABC News Sydney (@abcnewsSydney) January 14, 2016

“Colleagues, A security threat has been received by NSW Police which they advise may involve the Opera House. Police are on site currently assessing the situation. The site has been closed to the public,” the email said.

“This afternoon’s performance of Stick Man has been cancelled and Tours, Creative Play and SATH have been cancelled until further notice.

“Members of the public have been asked to leave the site while Police assess the situation.

“NSW Police advise that SOH staff and contractors may remain in the building during this time. Staff are asked to keep their passes with them at all times.

media_camera NSW police officers are seen in front of the Opera House in Sydney (AAP Image/Dan Himbrechts) NO ARCHIVING

“Any staff who would prefer to leave the site are free to do so in consultation with their managers.

“Pitt Street and Customs House should remain in their offices until more information becomes available.

The Incident Management Team are located in the Event Control area. We will continue to update as information comes to hand.”

Another employee posted: “I’m inside the Opera House as an employee, there is no news for staff either just that a security threat was received and police operation is under way.”

The Opera House has since advised that Opening Night event for Blanc de Blanc will still go ahead.