Beware 'backward steps': Premier warns Victorians to act responsibly

"All of these things - they can seem simple and very small but they all add up to what we have built - something that is precious but something that is fragile.

Mr Andrews urged Victorians to get tested as soon as they realise they have symptoms, and not have more than one pair of visitors to your home this weekend.

"We all have to play our part to protect it, to safeguard it and to make sure that we don't have to take any backward steps," he said.

Chief Health Officer Brett Sutton said the onus was on business managers to enforce rules and require compliance.

Professor Sutton said individuals would need to do the right thing personally, but also be willing to "call people out politely but appropriately" if they’re doing the wrong thing or turn them away from their homes if the visitor is sick.

"It will not be zero for any of us in Australia until there is a widespread use of a vaccine that is effective," he said.

"We do have to recognise that if we put aside all of those behaviours that we know have worked in stopping transmission, we put everyone at risk again.

"It is not about being mean. If you have a kid who has a cold at the moment, they shouldn't be going out. If you have developed a new cough, a new sore throat, a new fever, you shouldn't be going out. Everyone needs to play their part."

Two cases are 'weak positives'

It comes after the state enjoyed a brief run of zero-case days on Monday and Tuesday before two cases were reported on Wednesday and three on Thursday.

Professor Sutton two of the positive cases reported on Friday morning were "weak positives" that will be reviewed by an expert panel.

In a Twitter post, Professor Sutton said another of the four new cases was someone who previously had the virus and had likely recovered, with one case still under investigation.

Melbourne residents will enjoy their first weekend with newfound freedoms, but there will be no crowds at Flemington for Derby Day and traditional Halloween trick-or-treating is off the cards on Saturday.

The 14-day statewide average has risen slightly to 2.6, up from 2.4 on Thursday. But the number of mystery cases has fallen to two, down from four, for the fortnight to October 27.

He said while the state was not going for the elimination of COVID-19, it could "happen by virtue of finding everything that is out there" and was possible.

"We aren't hanging our hats on that because there could be hidden cases, chains of transmission that just go on without being detected as well," he said.

"If we can find each and every case that identifies the chains of transmission and use the isolation and quarantine in that broad contact tracing that has been done to stop it all, fantastic."

The state officially recorded three new coronavirus cases on Thursday, but two are suspected of being instances of viral shedding from old infections. One mystery case with no known source was confirmed on Thursday in Heidelberg West.

A young child connected to Melbourne's northern suburbs COVID-19 cluster was among the three cases, with a childcare centre closed and more than 100 people in isolation.

The child attended the Good Start Early Learning centre on Plenty Road at Bundoora, in Melbourne's north-east, on October 20 and 22. The girl's mother tested positive on October 25, and the girl was quarantined with her family from that date.

Twelve close contacts at the centre, including eight children, have been tested. By Thursday, six children and three staff had tested negative.

Friday’s four new cases were discovered in the local government areas of Wyndham, Brimbank, Hume and Greater Dandenong.

There were 23,583 tests completed across Victoria on Thursday. There are just 80 active cases across the state, with all of them in metropolitan Melbourne.

Five people remain in hospital with the virus, but there is no-one currently in intensive care.

Five healthcare workers are positive with COVID-19. There are now just four people connected to aged care in Victoria that have a positive case of the virus.

As Melbourne prepares for its first post-lockdown weekend, industry heavyweights have urged businesses to follow COVID-safe plans and avoid risking a third wave of the pandemic after photos emerged of some outlets flouting rules when they reopened this week.

Around Melbourne on Wednesday night and Thursday, some people were seen in pubs sitting shoulder-to-shoulder and not social distancing.

Last month – with the government under pressure to relax the lockdown – the Victorian Chamber of Commerce assured authorities that businesses would "take every precaution to prevent" a third wave, and that the hospitality industry should be "trusted" to operate safely.

The chamber's chief executive Paul Guerra said businesses and customers had a responsibility to follow the rules and return to a COVID-normal economy.

"If they continue to exploit the rules, not only would they be outed on social media, they can expect their customers to drop, and worse they can expect relevant authorities to [enforce the rules]," Mr Guerra said.

"No one wants to envisage a third wave, and the only way we can protect against that, is businesses and everyday Victorians doing the right thing."

An Ipsos poll commissioned by The Age and Nine News has found that Victorians are most worried about a third wave of the coronavirus and a further lockdown when thinking about next year, and more than half say the pandemic has affected their mental health.

The poll also shows COVID-19 had disproportionately affected young people’s mental health, with three-quarters of those aged 18 to 24 saying it had been impacted.