Dozens of "mystery" cases across Victoria have forced the state government to hold crisis talks about imposing further restrictions as soon as tomorrow.
Victoria is eyeing further restrictions as the state continues to record hundreds of cases a day.
Premier Dan Andrews told reporters this morning that "today is not the day to announce further steps" but admitted the government was discussing a number of options to slow community transmission.
The announcement comes as the reports claim Andrews has set Sunday as the deadline for a decision to be made on further restrictions, with health authorities reported to be working through the night "crunching data" to determine exactly what the next steps should be.
Andrews said the thing that was fuelling the restriction discussion was today's 49 "mystery" cases.
Of the 397 cases announced today, Andrews said there were 49 that health officials "simply cannot trace back" to where they came from.
"We are giving due consideration to a whole range of different options, when I am in a position to announce decisions I will do that," Andrews said.
"Forty nine doesn't seem a very large number but I just say to all Victorians that 49 where you can't be certain how they got it, that can mean there are many more than 49 out there that have very mild symptoms or no symptoms at all, they can be at the height of their infectivity, and be infecting other people unbeknownst to them.
"That is the real challenge here. It is a silent enemy, it is a very cunning enemy as well. But particularly those community transmission cases are of greatest concern to us.
"That is why we find ourselves in a position to evaluate these things and we can't rule out further steps being taken, they are being taken because that is what is necessary."
The premier also commented on recent calls from the Australian Medical Association to close supermarkets across Victoria, something Andrews said he was "considering".
"I'm trying to be as frank as I can be ... There is a lot of work going on because this is not easy," he said.
"If you take further steps you need to think it through properly and that changes to the rules will deliver the desired outcomes and that is a circuit breaker to try to pull this up."
The premier said enforcing further restrictions wasn't as simple as people think and reminded Victorians that any decision the government made would likely have massive ramifications for people.
"It is not a tap you can just turn on or off and they are not decisions that would be taken lightly because there are significant costs. Even minor changes have a significant cost," Andrews said.
"But the numbers are too high and there is a growing case for us to do more. What we may be doing now may not be enough when you consider that it has brought us stability.
"As [chief health officer Dr Brett Sutton] indicated yesterday, these settings, as challenging as they are, have avoided thousands and thousands of cases every day and the health system being overwhelmed.
"That should not be read to be people are doing it easy, it is tough and aged care is especially challenging. But we cannot open up again at these levels and, therefore, there is detailed work being done about possible next steps."
Greater Melbourne and the Mitchell Shire have been in a six-week lockdown since July 9, due to end on August 19.
Nine reported Andrews and Prime Minister Scott Morrison were in a call on Thursday night and discussed introducing tighter lockdown measures, such as those imposed in New Zealand.
From 11.59pm on Sunday, everyone in Victoria will need to wear a mask or face covering when they leave home to protect against the virus.
The updated restrictions brought the state's regions in line with Melbourne and surrounds.
Victoria reached a record 532 cases last Monday but this figure was quickly surpassed with 723 infections on Thursday and 627 yesterday.