An additional six new local cases of COVID-19 have been detected in Victoria on top of the five already reported on Monday morning, Acting Premier James Merlino has revealed.
Concerningly, cases have now been reported at two aged care facilities - two staffers and a resident at the Arcare aged care facility in Maidstone, and a worker at a BlueCross home in Sunshine.
There are now 51 cases in this community cluster, and Merlino says public health teams are in the process of "urgently investigating and interviewing" the newest members.
"In the past 24 hours we identified many more points of concern," Merlino told reporters at a press conference on Monday afternoon.
"In addition to the very worrying cases in private aged care, we are very concerned about the number of other high-risk exposure sites. We are seeing a small number of cases infecting a large number of contacts.
"There is no doubt, the situation is incredibly serious. The next few days remain critical. I want to be very clear with everyone, this outbreak may well get worse before it gets better."
It comes just a day after a worker at the Arcare facility was revealed to have become infected, though how they contracted the virus remains a mystery.
"Worryingly, both the staff member who has recorded positive and one resident... appears to have contracted COVID," shadow government services minister Bill Shorten told ABC on Monday morning.
He said the infected residents had been given their first dose of the COVID-19 vaccine.
"It's only second-hand reports from the facility, but the people who are sick actually had had a vaccination, so you need two - one is not enough."
Residents in aged care facilities who contract COVID-19 are at higher risk of severe illness and more likely to have underlying health conditions due to their age and frailty, New Zealand's Ministry of Health says.
The ministry says the facilities are also more susceptible to "rapid transmission" of COVID-19.
There are now more than 270 exposure sites in Victoria.
The site that's perhaps most concerning to local health officials is the Arcare aged care facility in Maidstone, because there's a high risk to residents and it's not yet known how a worker there became infected.
The woman in her 50s has been labelled the first "mystery case" in this most recent outbreak in Melbourne, and contact tracers are still working to establish how she contracted the virus.