Authorities are desperately trying to contain a coronavirus outbreak linked to a butcher at Chadstone Shopping Centre after it spread to regional Victoria.
Victoria recorded 15 new cases of COVID-19 on Tuesday - it's highest daily total in nine days - and one death, bringing the state's toll from the virus to 807 and the national figure to 895.
Eight of the new cases are linked to known outbreaks, while seven remain under investigation.
Chief Health Officer Brett Sutton said 28 cases have been linked to the Butcher Club at Chadstone, up from 24 on Monday.
It consists of at least eight staff, 11 close contacts and four customers.
Two people in Kilmore, 60km north of Melbourne, have also tested positive after coming into contact with someone in the cluster.
"That just speaks as to how wildly infectious this virus is," Premier Daniel Andrews told reporters on Tuesday.
"One only has to spend a moment to imagine if Chadstone were open at the moment just how many more cases we might well be dealing with here.
"If there were not restrictions in terms of movement into regional Victoria, as there are, then who knows."
Professor Sutton said the outbreak was an "illustration" of "just how significantly (the virus) can spread far and wide".
"I don't think anyone really understands what a gargantuan task the contact tracing has been through this wave," he said.
"The average family size in Australia is about 2.5 people. We've made estimates that the average family size for the 20,000 cases in this second wave has been between six and 10 people."
"It's not twice as hard as the first wave, it is 10 times as hard as the first wave in terms of the challenges of following up these cases."
One of the Kilmore cases is a worker at the Oddfellows Cafe, where a person connected to the Chadstone outbreak dined on September 30.
The diner was unaware they were COVID-positive at the time and had a permit to be in the region, but they were not allowed to eat in at a cafe as per the state's restrictions.
"(Melburnians) can only get takeaway food or drink. You can only go for the purposes of your work and those other essential things that you might require," Professor Sutton said.
He said it was up to Victoria Police if they wanted to fine the person.
The Kilmore cases are being considered as a separate outbreak for logistical reasons.
Melbourne's 14-day case average has dropped to 10.6 from 11.6 on Monday and its number of mystery cases between September 20 and October 3 is 13.
The city needs a 14-day average of fewer than five cases as well as fewer than five mystery cases before it can further ease restrictions.
Asked if Melbourne would meet the targets by October 19 as planned, Professor Sutton replied: "I really can't say".
"We can get to a point where there are significant numbers of cases every day and it drops off dramatically because they're all being chased up, those other close contacts have been contained and then you suddenly see a decrease in numbers," he said.
Professor Sutton said no country in the world had gone through a second wave as successfully as Victoria.
"Nobody wanted to be here. Nobody wanted to go through a second wave. But we are at a point now where we could snuff this out," he said.
A drive-through testing site has been set up in the Chadstone car park for symptomatic customers and there is also walk-in asymptomatic testing.
A testing site will also be established in Kilmore.
There are 21 Victorians battling the virus in hospital, including one in intensive care.
Australian Associated Press