Harbour City Ferries has admitted the device found on a Sydney ferry that led to a Circular Quay lockdown actually belonged to the company.

Staff on board the ferry Friendship found bottles with protruding wires and filled with nails and liquid on Thursday and reported it to police, who placed Circular Quay into lockdown for two hours.

The area was soon deemed to be safe and was reopened in time for the afternoon peak.

Harbour City Ferries later confirmed the package was a training device, but said it was not recognised by staff as such.

Company CEO Steffen Faurby said it was not the role of staff to investigate suspicious packages and the staff who notified police did the right thing.

He has admitted the incident took place because of a communication mix-up.

Mr Faurby said the device was part of a training exercise, but that information was not passed on to either the police or staff onboard the ferry.

"Every drill and every exercise that we conduct ... there are lessons to be learned," he said.

"We will clearly learn lessons from this exercise as well, and work those lessons into the way we conduct drills going forward.

"I do appreciate that this has caused some disruption to customers, but we will always put public safety first."

Police said they were glad ferries reported the suspicious package.

Acting Deputy Police Commissioner Frank Mennilli said there will be a debrief over the operation, and the details of who knew what about the device will be revealed then.

"In all these situations there's always a debrief, and these are matters that will be raised at that time," he said.

"In the debrief you have not only the police response but the other government departments, so all of these matters will be discussed."

Acting Deputy Police Commissioner Mennilli said police were not involved in security training programs for every government department.

"Look, it depends; sometimes they're joint exercises, some it's about training their own people," he said.

"That's why we ensure that all communication, not only within the NSW Police Force, but all other agencies, either government or non-government is a two-way street, and we support each other in these difficult times."