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Victoria has recorded 25 new Covid-19 cases in a worrying sign that the state's sixth lockdown could be extended into next week. 

Of the new cases reported on Sunday, 13 were infectious while in the community. 

The figure adds to the growing number of Covid-19 positive residents who were not isolated over the weekend. Ten were announced on Saturday. 

Stay-at-home orders look increasingly likely to be extended in Melbourne beyond Thursday, when they are due to end, but that decision is a few days away.

Victoria has recorded 25 new Covid-19 cases in a worrying sign that the state's sixth lockdown could be extended beyond next week

Covid-19 fragments were also detected in wastewater, prompting health officials to issue an alert for several Melbourne suburbs.   

Carlton, Glenroy, Broadmeadows, Camberwell, Truganina, Williams Landing, and Sunshine West residents were told to get tested if they show flu-like symptoms. 

There are now more than 500 exposure sites spread across multiple Melbourne suburbs, including the Royal Melbourne Women's Hospital and Chadstone Shopping Centre. 

Eight mystery cases are yet to be linked from the City of Melbourne, Glenroy, Melton South, Middle Park, Brunswick West and Wyndham Vale, as well as cases in Newport and West Footscray that were identified earlier this month.

'We are very concerned about what we're seeing across Melbourne,' Health Department deputy secretary Kate Matson said on Saturday.

'We won't have unlinked cases if people come forward to get testing as soon as they possibly can, at the earliest sign of symptoms.'

The figure comes as a leading epidemiologist warned it was 'most unlikely' Melbourne's sixth lockdown would end as planned on Thursday

The city's stay-at-home orders are due to end at midnight on Thursday, but with another 15 cases reported on Friday - including four mystery infections - Professor Tony Blakely says the restrictions will likely remain

There were 32,286 Covid-19 tests conducted and 23,076 vaccines distributed in the last 24 hours. 

A swimming pool, hospital and spice store are among the new venues added to the state's growing exposure list.

The Broadmeadows Aquatic and Leisure Centre was visited by a positive case between 5:45pm and 7:15pm on August 5.

The VicRoads, in Melton, between 12:30pm and 1:30pm on August 5 and the Royal Women's Hospital's main entrance, in Parkville, between 7:25am and 8:00am and 10:00am to 10:35am on August 6.

The SK Asian Spices store, in Glenroy, was also visited by a case between 5:50pm to to 7:00pm on August 12. 

A leading epidemiologist has warned it was 'most unlikely' Melbourne's sixth lockdown would end as planned on Thursday.  

Victoria's five-day moving case average is up to 17.4 and the effective reproduction rate is at 1.4, meaning currently every Covid-19 case is infecting almost one and a half people. 

Covid-19 fragments have also been detected in wastewater prompting health officials to issue a high alert across several Melbourne suburbs

Prof Blakely urged Victorians to get vaccinated, adding that by Christmas around 80 per cent of the population should have received the jab and therefore restrictions can ease

The state has reported 13 mystery cases over the past three days, with about 20 per cent of all new local infections over that span not in isolation while infectious. 

The city's stay-at-home orders are due to end at midnight on Thursday, but with another 15 cases reported on Friday - including four mystery infections - Professor Tony Blakely says the restrictions will likely remain.  

'Given that we tried a short, sharp lockdown I was hoping now that all arising cases would be occurring amongst quarantining people,' he told 7 News.

'That's not what we see, so I fear we've got quite a way to go with this outbreak yet.'

He said mystery cases were of most concern because they showed there were other chains of transmission undetected in the community.

Prof Blakely urged Victorians to get vaccinated, adding that by Christmas around 80 per cent of the population should have received the jab and therefore restrictions can ease.

'Hopefully we'll have a nice Christmas before we open up next year and deal with incoming people,' he said.

'That's what I'm focusing on is getting to that 80 per cent vaccination coverage and hopefully a good Christmas and New Year.'

There were 32,286 Covid-19 tests conducted and 23,076 vaccines distributed in the last 24 hours

Victoria's five-day moving case average is up to 17.4 and the effective reproduction rate is at 1.4, meaning currently every COVID-19 case is infecting almost one and a half people 

But steps will need to be taken to ensure Melbourne's outbreak doesn't escalate to levels seen in NSW - which recorded 390 new infections on Friday.

Victorians need to restrict their movements as much as possible, the epidemiologist said, and live as if they are already infected with the virus.

'I've got a bad feeling about this one because of the fact there's those mystery cases out there,' he said.

'I think it's most unlikely we'll be out of lockdown by next Thursday.' 

Professor Adrian Esterman, an epidemiologist and biostatistician at the University of South Australia, agreed.

He said Melbourne will get on top of its Delta variant outbreaks, but not by August 19 when the lockdown is due to end.

'I would say it's highly unlikely,' he said on Friday.

Health authorities are urging Victorians not to delay getting tested, as concern grows about the number of cases in the community while infectious

The state recorded 21 new locally acquired cases on Saturday, with 10 of those active in the community while infectious, as Melbourne's lockdown continues

'There is a couple of reasons. The effective reproduction number is still quite high - you want to see that get towards one to feel a bit more comfortable - and the moving average is still going up.

'I don't think that lockdown will finish, if I was the Victorian government, until you're in single digits and no mystery cases.'

The grim warning comes amid a string of new exposure sites across Melbourne including the entire Chadstone Shopping Centre - the largest shopping mall in the country.

The centre was exposed to the virus between 4.26pm and 5.40pm on Saturday, August 7 with anyone visiting the mall between those times instructed to get tested and isolate until they receive a negative result.

The Ritz Mansions apartment complex has also been put on alert over several days from Friday, August 6 to Wednesday, August 11. 

Premier Daniel Andrews on Friday called for more young Victorians to get vaccinated as he announced all residents aged 18 and above can receive the AstraZeneca jab at all 50 of the state's vaccination hubs from Monday.

'It is the most important thing to come forward to get vaccinated, to play your part, to protect not just yourself but the people you love the most and give us the freedom all of us want,' he said.

'Getting to 70 to 80 per cent vaccinated is what we have to work towards and these one million jabs over the next five weeks are the best way that Victoria can make a contribution, not just to our state's fortunes, but to our national strategy.' 

The State Government aims to administer 200,000 vaccine doses a week between August 16 and September 19.  

The Chadstone Shopping Centre in Melbourne was exposed to the virus on August 7 from 4:26pm to 5:40pm

Melbourne's lockdown is due to end next Thursday at midnight but with a surge in mystery infections, experts are fearing restrictions will remain (pictured police are seen speaking to a Melbourne resident)

'There literally are a million reasons to get vaccinated,' Mr Andrews said.

'It's a powerful contribution that every Victorian can make.'

Three more drive-through clinics will also be set up in Melbourne's southeast, southwest and northwest, following the popularity of the Melton site in the city's far west, which also opened on Monday. 

Mr Andrews expects 60 per cent of Victorians will be vaccinated by the end of September. 

The head of Melbourne University's School of Population and Global Health Nancy Baxter said the continuing spread of cases in the city meant it was unlikely Victorians could travel interstate by the September school holidays.

'Maybe Tasmania or South Australia [would let Victorians in by then], but we'd probably need two weeks of looking like there's no cases before anyone would say okay to us,' she told The Herald Sun. 

'For the next three or four months we just need to accept there's no guarantee for interstate travel and plans.'

The future of the AFL grand final and the Spring Racing Carnival is also in jeopardy, with concerns crowds may have to be prevented or severely restricted. 

Chief Health Officer Brett Sutton said Friday's unlinked cases include a delivery truck driver who lives in Wyndham Vale, a person in Middle Park and a person in Roxburgh Park, who is possibly linked to a school where an outbreak has recently occurred. 

It's the third consecutive day the state has recorded mystery infections, with authorities also racing to find the source of four cases recorded on Thursday. 

There are two people battling COVID-19 in hospital, including one person in intensive care. 

Mystery Covid cases in Victoria could mean the state's coronavirus restrictions are extended for months. Pictured are pedestrians walking in Melbourne on Friday as the city endures its sixth stay-at-home lockdown