Infectious disease experts have warned that Victoria's coronavirus spike could easily spread to other states and territories across Australia.
At midnight on Wednesday, will revert to stage three coronavirus restrictions, in a bid by the state government to regain control over a growing epidemic.
As the Melbourne outbreak accelerates, UNSW epidemiologist Professor Raina MacIntyre said case numbers could rise in other states, despite efforts to bar Victorians from travelling across state borders.
"It could already be spreading, we just haven't detected it," she told SBS News.
"We haven't had a testing blitz in NSW, so there could be epidemics growing in Sydney that we don't yet know about."
Professor MacIntyre said the outbreak was not unexpected, with Australia likely to see virus flare-ups until a vaccine is widely available.
But she was worried some Australians appear to be "completely oblivious to the fact that there's a pandemic" as social distancing advice is being ignored.
Other experts shared her concerns.
"If you just walk through the streets of Adelaide's Rundle Mall, for example, you see lots of people totally ignoring social distancing," University of South Australia biostatistician Professor Adrian Esterman said.
"This is a recipe for disaster - it just takes a single person to light a fire and it can destroy a whole community."
Victoria has reported 780 new cases over the past seven days, the overwhelming majority linked to community transmission.
A second wave?
Australia successfully flattened the coronavirus curve in April and May, but there are still fears the country could experience a second wave of coronavirus cases.
Countries like Iran and , which were impacted early in the pandemic, reported a second spike in infections.
But it's not believed the current outbreak fits that definition yet.
"I think it's a second wave in Victoria, but not the rest of Australia," Professor Esterman said.
Griffith University Professor Nigel McMillan said a national second wave would "need to be in a much wider geographical location".
"I don't think we're in a second wave, but potentially this is the start of one," he said.
"I think the lesson from Victoria for the rest of Australia is that we really need to be keeping to the restrictions ... and not to flout them."
Driven by disadvantage
Melbourne health authorities said the second surge in infections has been driven in part by clusters in disadvantaged communities.
"In terms of the rapid increase in numbers, that has been faster than in wave one and in many respects, it is faster than in some other waves across the world," Victoria's Chief Health Officer Brett Sutton told reporters on Tuesday.
"I think that's a measure of some of the social disadvantage that's been intersecting with the transmission in this wave."
Nine public housing towers remain under full lockdown as tests are conducted on over 3,000 residents at risk of infection.
"Diseases tend to spread through disadvantaged communities mainly because they are more crowded," Professor McMillan said.
One of the nine public housing towers locked down by the Victorian government. Source: AAP
"The housing situation means they are more packed closely together ... Otherwise the virus is non-discriminatory."
There has also been criticism of the Victorian government’s efforts to inform vulnerable and linguistically diverse communities about the pandemic.
"Sydney has the same sort of social housing and the same sort of multicultural makeup and yet we don't see the same problem," he said.
"So Victoria has done something wrong here."
Travel risks
The lockdowns in Victoria come as state governments in Queensland, South Australia and the Northern Territory continue with plans to open up state borders to non-Victorian residents.
"I wouldn't hesitate to travel to Queensland or Tasmania or the Northern Territory," Professor Easterman said.
"In all of these jurisdictions, there is no COVID-19 - the risk isn't there."
But that's not a view shared by all experts, with Professor MacIntyre warning recent outbreaks have increased the risks of interstate travel.
"Travel is risky during a pandemic, particularly airline travel where there are lots of different people from lots of different places passing together in crowded quarters," she said.
"There's more disease in Australia, so it's more dangerous now."
Residents in affected public housing towers who need access to support and assistance should call the Housing Call Centre on 1800 961 054. If you need a translator, first call 131 450. Both services are 24/7. More information can be found .
People in Australia must stay at least 1.5 metres away from others. Check your state’s restrictions on gathering limits.
If you are experiencing cold or flu symptoms, stay home and arrange a test by calling your doctor or contact the Coronavirus Health Information Hotline on 1800 020 080.
