New research shows that under the current settings daily Covid-19 cases in New South Wales could peak between 1500 and 6,000 a day by early October.
The University of Sydney has used complex modelling to forecast the trajectory of the latest outbreak, factoring in the high infectiousness of the Delta variant, current lockdown settings and the progress of the vaccine rollout.
Using data available up until August 25, it found that if restrictions were fully lifted when 80 per cent of adults were vaccinated, infections could surge to 40,000 cases a day.
The modelling showed that in the following month, half a million people could become infected with the virus, even with continued testing, tracing, isolation, quarantine and international travel restrictions.
The stark figure supports the NSW Premier and Chief Health Officer's decision to keep some restrictions in place even after the 80 per cent vaccination threshold is reached.
While Gladys Berejiklian hasn't outlined exactly which restrictions will stay, Dr Kerry Chant earlier this week flagged that mask wearing might remain "for years" to battle Covid-19.
Study lead Mikhail Prokopenko said the data was a cautionary tale.
"Although it is encouraging that more people are being vaccinated, we can expect to see a rapid increase in cases when we exit the lockdown."
He said it's expected that the lockdown will be lifted in NSW in November, once 80 per cent of the eligible population have received both jabs.
He wants to see social distancing remain in place to prevent a sharp peak in cases.
"In fact, our modelling suggests the worst is yet to come if the restrictions are removed too soon and too abruptly".
Professor Prokopenko said the post-lockdown surge would likely be in unvaccinated people, including children, and is worried the hospital system isn't prepared for an immediate spike in cases.
"The clear take-away is this... as a society we can either choose to land softly or come to a dramatic crash landing," he said.
"This will depend on the community continuing its high vaccine uptake, people maintaining social distancing over the coming months, and our healthcare system preparing and bolstering itself to meet the surge of hospitalisations which will come after the lockdown."
Professor Prokopenko expects pandemic growth to slow from mid-December.
The modelling was created by the Centre for Complex Systems at Sydney University. It has been published online but has not yet been through a rigorous peer-review process.