An expert says there is "no way" Victoria's lockdown will end within three weeks as initially announced.

Victorians were expected to emerge from a six-week lockdown on August 16 but Melbourne University epidemiologist Professor Tony Blakely believes authorities will need at least two extra weeks beyond that to get coronavirus cases down.

Blakely told news.com.au that outbreaks in the aged-care sector have contributed to continuing high numbers and said there was "no way" lockdown would end within three weeks.

"Things have not gone the way we hoped," he said. "Numbers are still high because of essential workers. It will take longer to pull the numbers back because there are cases in so many different segments."

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While cases appear to be coming down, with 295 cases recorded on Wednesday after a high of 532 cases two days before, Blakely said it was too soon to say what it meant.

"It gives me hope, and indeed today's numbers are the first time my three-day average model sees it curve down," he told news.com.au on Wednesday.

"So I am cautiously excited and optimistic – but not prepared to emphatically say we have turned the corner."

Blakely said there was hope masks could be a game changer and authorities should know by the weekend whether this measure is making a difference.

"If they don't come down dramatically we need to rethink this through," Blakely said.

Another factor in the longer lockdown is the Prime Minister Scott Morrison's comments last week that Australia is aiming for "no community transmission", something that neither Victoria or NSW have achieved since the pandemic began.

While Morrison said the country was sticking with a suppression strategy rather than going for elimination, his comments indicate authorities will need to get cases down to very low numbers, or even zero, before restrictions are eased.

Victoria's chief health officer Professor Brett Sutton told reporters on Wednesday there were still about 50 cases of community transmission a day, where no known source could be found.

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"That doesn't sound like a lot, but we were at a point a month or so ago where we had single figures for community transmission," Sutton said.

If Victoria is aiming for "no community transmission" then Blakely believes lockdown will have to be in place for longer if the state did not go to stage 4 lockdown.

Instead "smart stage 3" restrictions would need to remain in place for a "considerable length of time".

Modelling that Blakely is working on suggests Victoria will be "lucky" if it only requires a two-week extension of its stage 3 lockdown.

"Superspreaders and other things can go wrong, but my reasonable guesstimate is we will be lucky if there is only a two-week extension," he said.

Blakely acknowledged the modelling produced a "wide range", which suggested lockdown could continue for as long as a couple of months.

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"It could take up to a couple of months, it depends on chance and how well we do on these measures," he said.

Victorian Premier Daniel Andrews briefs the media on conditions concerning the Covid-19 situation in Melbourne. Photo / AP
Victorian Premier Daniel Andrews briefs the media on conditions concerning the Covid-19 situation in Melbourne. Photo / AP

Asked about the possibility of lockdown finishing earlier than six weeks, Victorian Premier Daniel Andrews told reporters on Wednesday: "where we will be in another three weeks, none of us can tell".

"What we can be certain of is that if we all keep working together, if we all keep working hard, if we all keep following the rules, then this will be over sooner rather than later," he said.

"It will be later if we don't drive these numbers down.

"It will be later if we don't all understand that our contributions and individual decisions, the actions we take … have a very clear impact."

One of the factors that could make a difference to the length of the lockdown is the target authorities are working towards.

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It's unclear yet whether authorities will insist on getting cases down to zero before easing restrictions, or whether less than 10 cases each day would be low enough.

There are also some measures that could get cases down quicker.

"For example if you shut down all construction for a couple of weeks, this could help move things along so we do have some control over this," Blakely said.

Blakely said the lockdown may also have to be extended to the whole state, beyond just residents in Melbourne and Mitchell Shire, as cases were now popping up in regional areas.

He said this was not surprising given essential workers were being allowed to keep travelling.

'SMART STAGE THREE'

Blakely believes that if authorities don't want to introduce a more strict stage 4 lockdown given its harsh economic impacts, the current stage 3 lockdown could be enhanced to make it more effective.

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The state has already introduced the mandatory use of masks and Prof Blakely believes it's crucial to keep this going.

"According to modelling, stage 4 will get you results quicker but it's not as important as masks," he said.

A woman walks across Princes Bridge in Melbourne, Australia. Photo / Getty Images
A woman walks across Princes Bridge in Melbourne, Australia. Photo / Getty Images

He said authorities should also be scrutinising different sectors to see where outbreaks were happening, and to make adjustments on who is considered an essential worker.

Cases among workers in certain industries (such as Uber, taxis and bus drivers) should be grouped together so authorities could easily see if outbreaks were happening.

Blakely believes a surveillance system with better information on cases in individual sectors should be developed and this data should also be provided to the community.

More importantly, Blakely believes the Victorian Government should "turn the gaze" back on its own systems.

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"I think (Premier) Daniel Andrews is doing a really good job but he does tend to tell us off for not doing things right," Blakely said.

"The most important thing is to focus as much on the system, as on berating individuals."

This could include scrutinising the state's contact tracing system.

Blakely said research showed every hour gained from when someone was notified of a positive test, interviewed by authorities and had their contacts interviewed, helped.

"The system seems overloaded at the moment," he said. "If we can get all test results back in 24 hours that will help."

Blakely believes providing information to the public about things such as how long contact tracing was taking, as well as what targets authorities were aiming for, would get the community on board and help them take ownership of the process.

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He said authorities in New Zealand had provided information to the public when this was requested during its hard lockdown.

"The whole country felt like they were in the control room, they felt trusted with that information," he said.

Blakely believes Victoria should take the time to make a systemic plan, create targets and monitoring systems on government performance.

He said authorities should also be engaging with community leaders on how best they could reach marginalised members of the public.

"Not just berating them and locking them in towers," he said.

"The virus finds its way into lower socio-economic groups and they need to be brought into the tent somehow.

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"Allow these people to be part of Melbourne society in a more meaningful way and to take collective action.

"They will be where the virus hangs around and explodes again."