Melbourne will emerge from its COVID lockdown at midnight on Thursday as planned, despite four new mystery cases in the city.

But masks will remain mandatory everywhere outside the home as the city remains on high alert and public health teams try to trace the source of the latest infections.

Victorian authorities said the city’s freedom remained a “day-by-day proposition”.

It is also possible restrictions won’t be eased further as planned next week, depending on what investigations into the new virus cases uncovers.

The four infections are from a single household in Reservoir, in Melbourne’s north. None is a close contact of a previous case or has visited an exposure site.

“The risks of this virus will be a factor in our lives in the long term and in the short term so, in the short, that means we are moving ahead but we are on high alert,” Acting Premier Merlino said.

“The public health advice is very, very clear. We can only consider doing something like this based on continuing high-test numbers like the 23,679 tests that we recorded yesterday.”

Mr Merlino said masks were an easy requirement that would allow Melbourne to reopen.

“It is a logical and common sense step to take, and it allows all of the businesses we have outlined yesterday that they can open. Movements can happen. Students can go back to school,” he said.

“This is a small price to pay to make sure that we can proceed with this careful easing out of lockdown.”

Melbourne’s lockdown will lift as planned, despite the four new cases on Thursday.

Victoria still has 78 active coronavirus cases.

They do not include the woman and her husband found to have the virus while staying on the Sunshine Coast after leaving Melbourne during its lockdown.

The man was Queensland’s only new community case on Thursday. NSW, where the couple stopped at numerous towns on their way north, had no community cases.

Mr Merlino said Victorian authorities were yet to interview the couple, but expected to do so on Thursday.

There have been reports they were moving to Queensland for the man to take up a new job. That would have been allowed under Victoria’s lockdown rules that applied when they left in June 1, travelling through regional NSW to the Sunshine Coast, arriving on June 5.

Deputy chief health officer Allen Cheng said one of the pair checked-in at Craigieburn Central shopping centre on May 23, leading authorities to suspect it could have been the source of their infections.

“We have had nine cases linked to that shopping centre to date,” he said.

“[This] really highlights the value that we have in QR codes … and I
think this also reinforces the message we’ve been saying for several days now that anyone who has been to the Craigieburn Central shopping centre who has any symptoms should get tested.”

Queensland authorities said on Thursday the Victorian couple appeared to be at the end of their COVID infection, making the spread of the virus less likely.

Chief health officer Jeannette Young has stopped short of forcing vulnerable settings such as aged care and disability accommodation into lockdown.

“I don’t believe the risk is such that we need to do that for this particular outbreak at this stage,” she said.

Back in Melbourne, Dr Cheng said masks were an effective barrier against the spread of the virus.

“It’s a small thing we can do to help prevent infection, depending on how
we move around, he said.

“Depending on how things go in the next week – and as the last week’s cases have shown, it’s a day-by-day proposition – we may need to hold at current settings a little longer.”

There were 180 public exposure sites in Victoria on Thursday. That number is expected to rise as investigations continue into the latest cases.

New sites include:

• Marco Fine Food and Groceries, Reservoir
• BP service station, Thomastown
• Bunnings, Thomastown
• Coles, Bundoora Square
• See others as they are added here

Melbourne’s extended “circuit breaker” lockdown will still end at 11.59pm on Thursday. But Melburnians must remain within 25 kilometres of their homes, unless working or studying, caregiving or getting a COVID-19 vaccine.

The travel limits are designed to keep Melbourne residents out of regional areas over the Queen’s Birthday long weekend.

Restrictions will also ease further for regional Victoria from Friday.