Modelling suggests health system will cope, Prime Minister Scott Morrison says

Mr Morrison said authorities had been working on the modelling of expected infections in Australia, and would release the work on Tuesday.

It had shown that without the measures put in place 12 days ago, when venues were closed and social distancing rules imposed, infections would be double the current numbers, he said.

On Friday, Australia had 5274 cases. Mr Morrison said that would have been 10,500 without the partial shutdown.

"You're saving lives, you're saving livelihoods. And if you want to know how much, you only have to look overseas and see what is happening in other developed countries around the world," he said.

Mr Morrison said if measures stayed in place and intensive care capacity was boosted as planned, with extra ventilators, the health system would hold up.

"The trajectory is promising, it's encouraging," he said. "But there are no guarantees. This virus will write its own rules."

Chief Medical Officer Brendan Murphy said the growth rate was falling, with case numbers now growing at about 5 per cent a day, well down from the rates of more than 20 per cent a fortnight ago.

"The issue that worries all of us ... are those community transmissions, those cases which have been passed from person to person ... without a clear epidemiological link," he said.

There were about 300 cases in Sydney, 60 in Melbourne, 30 in Brisbane and smaller numbers in other states where the infection source was not known.

"That means there are people who have COVID-19 or who are incubating it who don't know it," he said.

"We are quietly pleased with the direction we're going but we cannot stop because those community transmissions are growing."

Globally, cases have passed one million cases, and Professor Murphy said the true number was probably five or 10 times higher, given limited testing.

In Australia, while there were "certainly undetected cases", authorities were confident they had "a pretty good idea of the size of our outbreak", he said.