Earlier in the week there was shock as 270 new cases were recorded in a single day in Victoria. That figure rose even higher to 317 new cases in the 24 hours to Thursday.

Those record figures were eclipsed again by Friday morning's numbers with 428 COVID-19 cases in the previous 24 hours, the highest number in a single day in any state or territory in the country.

Since the start of June, more than 3300 coronavirus cases have been recorded in Victoria, about one-third of the entire number of cases detected in Australia since the pandemic began.

The state's chief health officer, Brett Sutton, said Victoria had not yet turned a corner in its fight against coronavirus, despite widespread lockdown measures, saying further deaths are expected.

Read more: Victoria records two deaths, 217 new cases

For a brief moment, it looked as though Victoria was flattening the curve.

As recently as June 9, no cases were detected in the state with preceding days having fewer than five cases.

But a breach of hotel quarantine would spark a rise in coronavirus cases across Melbourne, sending Australia's second-largest city back into lockdown.

State health authorities have identified a number of cases in late May and early June that were linked to breaches of hotel quarantine procedures.

Reports have claimed security guards contracted to patrol hotel quarantine were having sex with guests and allowing families separated by quarantine measures to go between rooms.

Epidemiologist at the University of New South Professor Mary-Louise McLaws said the breach of hotel quarantine was like the start of a bushfire, with the virus then allowed to spread across the community.

"They had a perfect storm on three fronts. That was the breach in the hotel quarantine which was the spark of the bushfire, and then it gained fuel by then being spilled over into hyper-connected social and family groups," Professor McLaws said.

"That then spilled into retail outlets and places such as residential aged care facilities, and the case numbers all went up.

"This is a bushfire that is now raging."

Despite measures to try and control the spiraling number of cases through the lockdown of hotspot suburbs in Melbourne's north, that lockdown was then extended to the entire metropolitan area and the neighbouring Mitchell Shire area as new infections increased.

While the daily figures of new coronavirus cases has increased in recent days, experts have said the spike doesn't constitute a second wave of the virus just yet.

Professor McLaws said while the term had links with the Spanish flu pandemic almost 100 years ago, what was being seen in Victoria was not a second wave.

"I would call this a resurgence of the virus. Victoria was doing very well until this happened," she said.

"The second wave [during the Spanish flu] had to do with an introduction of a much more severe strain of the virus."

She said the number of cases has increased but there was no evidence of the virus being different to that seen earlier this year at the beginning of the pandemic.

At the start of the pandemic in Australia, a majority of the cases were from travellers returning from overseas where the virus had run rampant, such as China, western Europe, the UK and United States.

While there had been instances of community transmission in the first few months of the crisis, those numbers have soared in Victoria in recent weeks.

Professor McLaws said new virus cases had been linked to many clusters centred around indoor gatherings or large family groups.

"Social venues such as pubs and bars are the perfect environment for the virus, and it loves people being inside close together," she said.

"Many of these are super-spreading events, and the virus is amplified."

In the past week, the number of new virus cases linked to being acquired overseas has been as low as just 3 per cent.

"There was the indication of a problem with new cases around June 18," Professor McLaws said.

"Then in 14 days time, or one incubation cycle of the virus, the number of cases had increased fivefold."

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At Victoria's daily coronavirus update on Friday, chief health officer Brett Sutton said the state had not turned a corner, calling the situation disappointing and concerning.

"There will be dozens of individuals who will require hospitalisation from these 428 [cases]," he said. "Tragically, there will be several who require intensive care support and a number of people will die."

It's been a little more than a week since all of metropolitan Melbourne was placed under stage three lockdown measures, with hotspot suburbs being in lockdown for almost a week longer.

Health officials have said it would take several weeks before it was known whether lockdown measures had helped to reduce the number of new cases, with the average incubation period of coronavirus being around 14 days.

Professor McLaws said at current rates, it did not look like cases in Victoria were going down, but the picture would be clearer after further figures were released in coming days.

"In the next five days, we'll know whether the curve has started to flatten," she said.

"Hopefully in that time the virus would have slowed and not head upwards further."

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