Victoria has reported one new locally acquired case of coronavirus after four people tested positive for Covid-19 on Monday.
Deputy Premier James Merlino told reporters on Tuesday a man in his 60s who tested positive was linked to the four cases – a man in his 30s, a man in his 70s, a woman in her 70s and a pre-school aged child, all from the same family across three households in Whittlesea, in Melbourne's north.
Mr Merlino said he was isolating along with his household contacts.
Chief Health Officer Brett Sutton said the man was showing symptoms when he had a business appointment with the man in his 30s who tested positive.
Professor Sutton added the transmission likely occurred on May 18.
The new case comes after Melburnians were being warned undetected cases could have been "quietly cooking away".
Health authorities have been scrambling to identify how the family contracted the virus, with questions over whether or not it could be linked to an earlier case.
Head of the vaccine and immunisation research group at the Doherty Institute, Professor Terry Nolan, told 3AW radio in Melbourne the new cases were likely linked to a Wollert man who tested positive earlier this month.
“I hope it is linked and I hope we haven’t found another cluster or another chain that has been quietly cooking away there in the background," Professor Nolan told 3AW.
“I think it’s more likely than not it will be connected, but it may not be, so brace yourself everyone.”
One of the Whittlesea cases reported Monday did visit the same Woolworths as the Wollert man, but he only attended the supermarket after the previous case was already in quarantine.
"We do not rule out the prospect that there is a link," Health Minister Martin Foley said.
"The dates do not line up immediately so we cannot rule out if there is a missing link out there."
Mr Foley added on Tuesday the fifth case has not identified any link to exposure sites from the Wollert case.
Professor Sutton also warned there could be other cases out there.
"It is possible there is another missing link," he told reporters.
"We do have to conduct an interview with case five today and if there is an identified crossover with an exposure site it would be reassuring but there may be other cases out there."
Melbourne faces new Covid restrictions
Mr Merlino announced a number of new restrictions for greater Melbourne in effect from 6pm tonight.
Private gatherings in greater Melbourne will be limited to five people while public gatherings will be limited to 30.
Face masks will also need to be worn indoors unless an exemption applies.
Mr Merlino said a mask was required for everybody aged 12 and over.
Schools and workplaces remain open and Victorians who live in greater Melbourne can still travel to regional Victoria. However, they will still have to follow rules as if they were in greater Melbourne.
Victoria Chief Health Officer Brett Sutton said the first positive man in the Whittlesea cluster was carrying a high viral load and warned the community to brace for more possible cases.
"He is likely to be quite infectious," Professor Sutton said.
"We have to ready ourselves for any other positives, and when there are close contacts who do become positive, that raises the possibility that even a casual contact could become positive as well."
The latest outbreak snapped Victoria's 86-day streak without a locally acquired case.
More exposure sites listed
Victorian health authorities now have identified 10 exposure sites as they race to contain a Melbourne Covid-19 outbreak.
They hope genomic sequencing will establish the source of four new Covid-19 cases among a family in the city's north.
Nando's Epping and Woolworths Epping North joined Jump! Swim Schools Bundoora and Highpoint Shopping Centre as tier one sites, meaning anyone who attended those places at specified times must be tested and isolate for 14 days.
Futsal Brunswick, Epping North Shopping Centre, House and Party at Epping, Urban Diner Food Court at Pacific Epping Shopping Centre, Shells Coles Express Reservoir and B.T. Connor Reserve are tier two sites – meaning affected people must get tested and isolate until they have a negative result.
Do you have a story tip? Email: email@example.com