Melbourne and regional Victoria will still move to eased restrictions with one small exception, despite the source of a new COVID-19 cluster remaining unknown.
Acting Premier James Merlino confirmed the relaxing of rules will proceed as planned from 11:59pm on Thursday, albeit with a slight change of mask rules for Melbourne.
Masks had been poised to become non-compulsory outdoors, unless physical distancing was not possible, but now will have to be worn under all circumstances.
"It is inconvenient but an easy thing to do," Mr Merlino told reporters ahead of the city's lockdown lifting.
"We are used to it, we know it works."
Deputy Chief Health Officer Allen Cheng said four new cases reported on Thursday were all from the same household at Reservoir in Melbourne's north.
The family members are not primary close contacts and hadn't visited any listed exposure sites, leaving contact tracers racing to find a missing link to existing outbreaks.
"We are still in early days at looking at this cluster in Reservoir," Professor Cheng said.
"We would be more comfortable if we could identify a link ... to another cluster."
A man in his 80s was the first family member to test positive on Wednesday.
He developed symptoms on Monday and was tested the next day, with the short window meaning only four initial "tier two" exposure sites have been linked to the family unit.
All four are in Melbourne's outer north and include a Coles at Bundoora Square and a Bunnings at Thomastown.
Prof Cheng said none of the household members, which also includes a woman in her 70s and two men in their 50s and 20s, were in hospital.
One is on the disability pension, while another provides care for them but does not work at a disability facility.
Several of their close contacts have returned negative tests so far, though will still have to remain in isolation.
Meanwhile, state health authorities are preparing to interview an infected Melbourne couple who prompted separate COVID scares in Queensland and NSW.
A woman left Melbourne with her husband on June 1, when the city was in lockdown, and tested positive at the end of a road trip through NSW and into Queensland.
Her husband has now tested positive as well and it appears both are late in their infection period.
"It is important to note that if they were relocating it is not a breach of directions here in Victoria. But we just don't know," Mr Merlino said.
While unable to initially pinpoint a possible source of their infections, Prof Cheng said one of the cases had checked in near the Craigieburn Central shopping centre on May 23.
There have been nine cases linked to the shopping centre in the city's north.
"The fact that we've been able to identify a possible link to the Craigieburn shopping centre within hours of hearing about these cases and even before being able to speak to these cases, really highlights the value that we have in QR codes," Prof Cheng said.
Victoria's COVID-19 commander Jeroen Weimar said 1500 primary close contacts had been cleared in the past 24 hours, as the number of exposure sites fell from more than 350 to below 140.
There are 78 active cases across the state, down five from Wednesday.
Some 23,679 Victorians were tested on Wednesday and 20,784 received a vaccine dose at state-run sites.
