Responding to questions by Greens Senator Sarah Hanson-Young, immigration officials revealed that from July to September this year, detention centres at Nauru and Manus Island cost almost $280 million. This includes payments to Transfield Services, the contractor who operates the centres on behalf of the Turnbull government, and capital and refugee resettlement costs.

As of October 15, there were 92 child asylum seekers and 87 child refugees at Nauru.

Mr Pezzullo and Mr Quaedvlieg told the hearing they took responsibility for the botched Operation Fortitude operation in Melbourne, and a press release that said immigration officers would be "speaking with any individual we cross paths with".

Mr Pezzullo said the press release contained "inopportune and imprudent wording" and Border Force officials did not have the power to, and never intended to, roam the streets "checking people's papers".

But a series of "talking points" to be used by Border Force spokespeople ahead of the operation, which were tabled at the hearing, reiterated the press release, saying "we will be speaking with a range of individuals we come across".