Australians have been given an insight into how bad the coronavirus outbreak could have become if the Morrison Government had not acted.
Prime Minister Scott Morrison revealed on Tuesday details of the early modelling his government used to manage its response.
Morrison stressed the "highly theoretical" modelling presented a "worst-case" scenario based on overseas data.
"What is absolutely clear is that if we relaxed any of the current measures, that would turn into an explosive outbreak driven by community transmission and we would be in a very poor situation very quickly," the Age reported University of Melbourne professor James McCaw as saying.
Measures Australia has put in place have already reduced infection rates to a much lower rate than predicted.
Non-peer reviewed papers by the Doherty Institute, looked at possible infections from overseas, and at modelling initially developed in preparation for a influenza pandemic to simulate impacts on Australia's health system.
The latter highlighted the pressure on Intensive Care Unit beds without strict social distancing measures.
Several scenarios were modelled, including an "incredibly unlikely" worst-case scenario where nothing was done to stop the spread of coronavirus in Australia. Doing nothing would have resulted in 23 million people getting infected all at once and would have completely overwhelmed the hospital system. Only 15 per cent of people who needed ICU care would have been able to access a bed.
Had Australia stopped at isolating sick people and quarantining others likely to be infected, an estimated 67.5 per cent of Australians would have been infected and only 30 per cent of those who needed ICU care would have been able to get it.
The paper noted that if ICU beds were doubled, this would still only meet between 10 and 30 per cent of demand. Increasing bed numbers by five times would also fall short, covering between 20 and 40 per cent of demand.
"Case isolation and contact quarantine alone will be insufficient to keep clinical requirements of Covid-19 cases within plausibly achievable expansion of health system capacity," the report said.
To ensure 100 per cent of those who need ICU care would have access to a bed, social distancing restrictions would be required, it said.
"A combination of case-targeted and social measures will need to be applied over an extended period to reduce the rate of epidemic growth."
However, it also noted that the "social and economic consequences" of such measures would limit how long they could be kept in place.
"In reality, it is likely that the stringency of imposed controls, their public acceptability and compliance will all vary over time," the report said.
It said further work would look at how the measures could be varied, to figure out "exit strategies" for relaxing stringent lockdown conditions.
The report also noted that the modelling was limited by ongoing uncertainty around the true disease "pyramid" for Covid-19, and the lack of information about why some people get a more severe form of the disease.
The modelling was based on international data. Morrison said on Tuesday the modelling proved the theory of "flattening the curve" and that measures Australia had taken could make a difference.
"We are on the right track.
He said the Government would be doing more modelling based on Australian figures, although the small number of cases mean there were not enough as a base. "The National Cabinet fully understands the limitations of this work," he said.
Chief medical officer, Professor Brendan Murphy said authorities now had data on nearly 6000 Australians and it was hoped there would be some useful insights in the next few weeks.
However, he noted that fewer than 100 people were in ICU in Australia and fewer than 40 were on ventilators, which is "quite a low rate of serious disease".
"Our current case rate is very, very low. Every death is a tragedy, but our death rate is one of the lowest in the world so far," he said.
"We don't know what it will be as the disease progresses, but we are reassured to some extent about that.
"The most important message from this model is we know that the tools we are using work, and we can scale them up and down as necessary."