Up to 200,000 cases a day could be reported across Australia by late January to early February without medium-level restrictions.
Hospitalisation rates could reach up to 4000 a day if the virus continues to spread rapidly.
The modelling is based on little to no restrictions where there is no lockdown, low-density requirements, no retail restrictions, and schools stay open.
It also assumes that the Omicron variant is more transmissible than the Delta variant and also causes severe illness.
The modelling showed a hard lockdown could suppress a serious outbreak in a month’s time if most Australians receive all three vaccine doses by that time.
Prime Minister Scott Morrison on Tuesday insisted Australians would not undergo another hard lockdown.
“We’re not going back to lockdowns,” Mr Morrison said.
“We’re not going back to shutting down peoples’ lives.”
“We’ve got to let Australians make their own choices about their own health and their own lives.”
Mr Morrison wrote in a letter for the leaders ahead of the meeting that it is imperative for Australians to take responsibility for their own health during the rise of COVID-19 cases.