Experts have warned Australia's coronavirus cases could soar further as the nation braces for infection records to be smashed.
Burnet Institute director Brendan Crabb said modelling showed daily cases could jump to between 3000 and 4000 within 30 days unless urgent steps were taken.
"We're in now what is a national emergency," he told the Nine Network on Thursday.
"We're in a steam train that is heading towards a cliff, not heading towards a station which is where we should be going."
Professor Crabb is urging the NSW government to implement uniform restrictions across all areas of Sydney including a curfew and five-kilometre travel limits.
He believes immediate action coupled with more generous support for workers and business could turn the situation around.
"The worse case scenario is we have an Italy-style health catastrophe. That is actually the trajectory at the moment," Professor Crabb said.
"The best outcome is lockdown until sort of Christmas.
"Now, I don't know how on earth they would keep numbers as they are now, because we are doubling every 11 days."
One Covid case is infecting three others
Coalition for Epidemic Preparedness Innovations chair Jane Halton said she has been lying awake at night thinking about how to stop the virus.
"Every person who's got this disease is on average transmitting it to 1.3. So, sadly, the numbers are marching upward and we're not seeing them come down," she told Nine.
She said understanding why people continued to move around despite restrictions, and providing financial incentives to stay home were crucial.
"We need a carrot and we need a stick," Ms Halton said.
Deputy Chief Health Officer Sonya Bennett is more upbeat about case numbers falling.
“We’re in a steam train that is heading towards a cliff, not heading towards a station.”
Professor Brendan Crabb from the Burnet Institute is imploring NSW authorities to change their strategy to the growing Delta outbreak. #9News pic.twitter.com/iPkQZJVPmr
— 9News Australia (@9NewsAUS) August 18, 2021
"We're really expecting to see and anticipating that we will see a decrease in those numbers shortly," she said.
Victoria recorded its highest new case number of this outbreak, as Melbourne had its 200th day in lockdown since the pandemic begun.
But 54 of the cases have been linked to existing chains and 44 were in isolation throughout their infectious period.
The ACT is also grappling with a coronavirus outbreak with territory's tally hitting 83 cases on Thursday as infections cluster around schools, bus and light rail routes, and childcare centres.
Melbourne and Canberra will be in lockdown until at least September 2, while the future in NSW is even more clouded with regional outbreaks sparking major concerns.
Do you have a story tip? Email: firstname.lastname@example.org.