All passengers who arrive in Australia after midnight on Saturday will go into mandatory quarantine in hotels for a fortnight, Prime Minister Scott Morrison has announced.

Key points: Passengers will be quarantined in the city they land in, irrespective of where they live

Passengers will be quarantined in the city they land in, irrespective of where they live Two-thirds of Australia's coronavirus cases are from people travelling from overseas

Two-thirds of Australia's coronavirus cases are from people travelling from overseas Defence personnel will help state and territory police enforce self-isolation rules

Concerns have been raised about people not adhering to self-isolation requirements, particularly after getting off cruise ships.

Defence Force personnel will be brought in to support state and territory police in enforcing the mandatory quarantine and the self-isolation rules that apply to people who are already in Australia or who arrive before the Saturday midnight deadline.

Mr Morrison said two-thirds of the nation's confirmed cases of coronavirus had come from people travelling from overseas.

"States and territories will be quarantining all arrivals through our airports in hotels and other accommodation facilities for the two weeks of their mandatory self-isolation before they are able to return to their home," he said.

"If their home is in South Australia, or in Perth, or in Tasmania and they have arrived in Melbourne, they will be quarantining in Melbourne."

A long queue of passengers waiting to check in for a flight at Sydney International Airport. ( AAP: James Gourley )

The forced quarantine rule was agreed to at National Cabinet, a meeting of the Prime Minister, premiers and chief ministers, on Friday morning.

"We will not take these decisions lightly, we will not take them for a matter of convenience," the Prime Minister said after the meeting.

Mr Morrison said the head of the federal Treasury Department also briefed leaders about the economic impact of the coronavirus pandemic.

Stay up-to-date on the coronavirus outbreak Download the ABC News app and subscribe to our range of news alerts for the latest on how the pandemic is impacting the world

He said he expected to announce a plan to help hibernate Australian businesses, so they could survive the economic downturn, in coming days.

"The idea is simple — there are businesses which will have to close their doors," the Prime Minister said.

"They will have to keep them closed either because we have made it necessary for them to do so, or simply there is just not the business to keep their doors open.

"We want those businesses to start again. And we do not want, over the course of the next six months or as long as it takes, for those businesses to be so saddled by debt, so saddled by rental payments, so saddled by other liabilities, that they will not be able to start again on the other side."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 48 minutes 32 seconds 48 m Watch Prime Minister Scott Morrison give an update on coronavirus pandemic in full

Australia fighting economic and health crisis, PM says

Mr Morrison said Australia was battling coronavirus on two fronts and warned the economic impact could prove even more deadly than the health crisis.

"Both will take lives, both will take livelihoods," he said.

The Federal Parliament approved more than $84 billion in stimulus measures on Monday as the coronavirus continued to wreak havoc on the economy.

But the Government appears set to go even further, with the Prime Minister confirming he and the Federal Treasurer were in the final stages of a third economic stimulus package.

The first two have included additional support for small businesses and a doubling of Jobseeker welfare payments to assist the forecasted 1 million people who will lose their jobs.

National Cabinet will continue to work on plans to offer rent relief, with states focusing on residential assistance and the Federal Government devising a plan for small business rent.

Under plans being considered, banks, lenders and landlords would all be asked to wear some of the pain, waiving all overheads including rents and mortgage repayments for at least the next six months.

Further shutdowns loom

There are estimates of an 80 per cent drop in the number of people moving around Australia's major cities.

That came after National Cabinet twice in the last week enforced major shutdowns that saw the closure of pubs, clubs, places of worship, indoor sport and entertainment facilities.

"There will be a stage three. That is not today but there will be a further stage," Victorian Premier Daniel Andrews said after the Cabinet meeting.

Leaders have urged people to remain at home unless it is essential for them to leave for work or to go to the shops.

Mr Andrews said he hoped the nation's leaders would reach an agreement on what that next stage of shutdowns might include.

The Prime Minister thanked Australians for adhering to new physical-distancing crackdowns, where people are to keep 1.5 metres apart, but said the nation would have to go further.

"Let's keep doing the right thing, let's keep saving lives, let's keep saving livelihoods," Mr Morrison said.