No federal department is squarely responsible for the nation's quarantine, the Department of Prime Minister and Cabinet says.
Senior official Alison Frame has also claimed full capacity at the NT's Howard Springs quarantine facility would be "very difficult to ever actually realise".
Appearing before the Senate's COVID-19 committee on Friday, Ms Frame revealed no Commonwealth body took overarching responsibility Australia's quarantine system.
"Different departments lead on different aspects of quarantine. " she said.
"So the quarantine system we have at the moment does reflect different oversight, but it comes together in terms of the Commonwealth providing integrated advice.
"We integrate information across the government, and provide information to the Prime Minister."
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To illustrate her point, Ms Frame said requests on international students were passed to Education Minister Alan Tudge, though the Infrastructure Department was responsible for overseeing passenger caps.
Labor senator Katy Gallagher summarised her responses as no department being "in charge".
"That's correct," Ms Frame replied.
There were 38,523 Australians registered with the Department of Foreign Affairs and Trade as wanting to return home, including 4,569 vulnerable people and 438 unaccompanied children.
Over 10,000 were stranded in India, where flights returning Australians were temporarily grounded in May as New Delhi grappled with the world's worst Covid-19 outbreak.
DFAT revealed there were 18 flights scheduled this month for Howard Springs, host to 1,279 people, with India the "number one focus".
But Ms Frame poured cold water on the idea, conceding the its intake had not "ramped up as we had hoped" after the India travel pause.
"It would be very difficult to ever actually realise that full capacity at any point in time, [but] we could go very close," she said.
Flights were allocated a 200-space "neighbourhood", regardless of how many people were on board. Excess space was not filled by passengers from the next flight because each group was siloed.
Mr Morrison last month suggested sites for Commonwealth-supported quarantine facilities in WA and Queensland, having signed off on a similar proposal from the Victorian government.
Ms Frame insisted the Commonwealth was "urgently" augmenting the hotel quarantine system, which remained "fit-for-purpose".
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