Australia's borders have been closed to international travellers for weeks, with citizens and permanent residents returning to the country now required to isolate inside hotels for 14 days before being allowed in to the community.

A high percentage of Australia's confirmed cases of the disease continue to be linked to overseas travel.

How long Australia's borders remain closed depends on how fast a vaccine can be developed and rolled out to the population across the world, Professor Kelly said on Friday.

"If we have a vaccine which does work, and does give lasting immunity and can be rolled out across the world, not just in Australia, then that changes everything.

"Certainly the border closures will be a component of what needs to happen into the future."

Whether travel restrictions remain at current levels remains to be seen, and the Australian Health Protection Principal Committee was advising national cabinet on "various options" for the future and other considerations.

"We are an island, of course, and that's our advantage. But we also do need to have our trade both back and forth, to continue in the society that we love. So these are all elements that will be part of the road out, as the Prime Minister said.

"It's too early to talk about that road out for the time being."

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Border restrictions not only depended on what was happening overseas and in the race for a vaccine, but how successful Australia is at flattening the curve of infection of coronavirus, because if the disease "died out" it may leave the country vulnerable.

"In terms of the virus dying out, as it were, in certain parts of Australia, that would be a great achievement. It does bring with it a challenge, of course, it would mean the most of us would not have been exposed yet. So we would remain susceptible to the virus if it was re-introduced."

Australia was still only 14 weeks into the fight against coronavirus, Professor Kelly said, meaning it was too early to know if people who had contracted the virus then had long-term immunity.

Both Qantas and Virgin Australia have cancelled all international flights, although Qantas has been working with the government to charter rescue flights to assist Australians to get home from countries that have gone into lockdown, or that were stuck on cruise ships.

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