Contract tracers may be fighting a losing battle to contain Sydney's latest coronavirus outbreak with a lockdown appearing more and more likely, warns Australia's peak medical body.
Case numbers almost doubled for the second day in a row after 16 new locally acquired cases lifted the Bondi cluster to 37.
This has drawn parallels to how cases surged in Melbourne shortly before the city entered one of the world's longest lockdowns.
The rapid surge has alarmed experts, with Australian Medical Association vice-president Dr Chris Moy calling them "worrying" numbers.
He said the original strain of Covid-19 that forced Victoria into lockdown last June was not as contagious as the Delta strain that has gripped Sydney.
"This is one to worry about because the Delta strain is more concerning," Dr Moy told NCA NewsWire.
"The contact time is 10 seconds or fleeting contact and it is escaping hotel quarantine on repeated occasions and that is extremely worrying.
"There are parallels with the Victorian situation and this is occurring when there are very few restrictions."
He said not even NSW's "highly regarded" contact tracers may be able to nip this spread in the bud because it is so infectious.
"There is always this reliance on NSW on their highly regarded contact tracers, but even they would be very worried," he said.
"The bottom line is, if it keeps on escalating like this, it doesn't matter how good your contact tracing is, they will be looking at pulling the lever on a lockdown."
An outbreak at the Cedar Meats abattoir in Victoria saw a cluster of eight confirmed cases skyrocket to 90 over the course of 12 days in 2020, a report from the Royal Australian College of General Practitioners said.
By May 26, a manager at one of Melbourne's quarantine hotels tested positive, with five security guards and their families adding to that cluster.
Victoria moved to a stay at home order on June 30, when the state recorded 108 new cases.
NSW Premier Gladys Berejiklian brought in tighter restrictions on Wednesday including masks must be worn indoors and banned all non-essential travel outside of Sydney.
Monash University immunologist professor Alan Baxter noted the similarities in numbers ahead of Victoria's second lockdown.
"With a doubling time of around 24 hours, and 23 cases today, Sydney is now where Melbourne was exactly one year ago. Let's hope they learned from our example," he tweeted.
Professor Baxter told NCA NewsWire, "tomorrow's figures will make the situation much more clear."
If there is a saving grace, it's that aged-care residents are by and large vaccinated, Dr Moy said.
"The one good thing is, basically the vast majority of nursing home residents have been vaccinated and that is where a majority of the deaths occurred (in Victoria)," Dr Moy said.
Professor Peter Collignon, from the Australian National University Medical School, said NSW still had a way out of the rapidly spreading virus, noting the state's communication with the public on exposure sites was much more rapid.
The leading epidemiologist said NSW's early testing regime through rigorous contact tracing, which Victoria didn't have, was the reason for the rapid escalation in positive tests.
"It is different to Melbourne last year because they had fairly poor contact tracing," Professor Collignon said.
"There were places, like the abattoir, where there 100 cases and Victoria was not announcing the names of the places where this was happening.
"Victoria only got into real problems when they had 30 or more cases a day and it's too early to make predictions on numbers."
He expected low double-digit positive cases in the coming days but was more concerned about unlinked community transmission.
"I'm not going to be surprised with 10 a day for a few days, but I hope that most of those will already be in isolation," he said.
"The number that worries me, is any community transmission cases that are unlinked and so far that has not been in high numbers.
"For every one you find that is not linked, there is another in the community you have missed."