Acting Victorian Premier James Merlino has confirmed a standalone quarantine hub will be built in the state – as he also dug in on Melbourne’s extended lockdown.

“I’m very, very pleased that today we have reached agreement, both the PM and I have signed a memorandum of understanding and we’re going to get cracking and deliver this facility,” Mr Merlino told a media briefing ahead of Friday’s national cabinet meeting.

It is not yet clear whether the centre will be built at the state government’s preferred site at Mickleham, north of Melbourne, or at Avalon, near Geelong, which the Morrison government favours.

“We have not yet landed on exactly which site, but either one will work,” Mr Merlino said.

Shortly after the Acting Premier spoke, Victorian health authorities confirmed four more virus cases on Friday. Victorian testing commander Jeroen Weimar told Melbourne radio all were in close contacts of other infected people, and all were already in isolation.

There are now 65 infections in the outbreak that is keeping Melbourne in lockdown.

Tweet from @VicGovDH

They do not include the two false positives confirmed by state health authorities late on Thursday. Mr Merlino said the mistaken diagnoses were unlikely to mean Melbourne’s lockdown was cut short.

“Our answer on that hasn’t changed and nor should it. It is absolutely based on public health advice and that is assessed day by day, hour by hour,” he said.

“The proposition put forward by public health was that we needed this further seven-day period for greater Melbourne to absolutely run this thing to the ground. That remains the case.”

The two suspected “fleeting” transmission cases of coronavirus were among the justifications for extending Melbourne’s lockdown.

Health authorities initially thought a woman caught COVID-19 at a Metricon display home at Mickleham, and believed a man similarly picked up the virus at Brighton Beach Hotel, in bayside Melbourne.

That was not the case, with an expert panel confirming neither was even infected.

“When you do hundreds of thousands of tests during the pandemic, these things happen. They have happened a number of times,” Mr Merlino said.

Victoria has set almost daily records for COVID testing during its latest outbreak, topping 50,000 on most days.

The COVID-free pair and their primary close contacts will be released from isolation and any associated exposure sites stood down, including in Anglesea along the Great Ocean Road.

The Metricon display home and Brighton Beach Hotel remain linked to other confirmed cases and will remain exposure sites.

Mr Merlino said there were still hundreds of public exposure sites across Victoria, and more than 5000 close contacts in isolation.

“The advice from public health remains the same. We needed to go into lock down to drive this variant of concern into the ground because we cannot risk – we cannot risk it running away from us,” he said.

“We can’t risk it for Victorians. Indeed, we can’t risk it for Australians.”

There are still eight cases in the current Melbourne outbreak where infection is blamed on “stranger-to-stranger” transmission.

The state’s chief health officer, Brett Sutton, has repeatedly described the Indian (or kappa) variant that is driving the current Melbourne outbreak as a “beast”. His deputy, Allen Cheng, has estimated it is probably 50 per cent more infectious than the strain that led to the city’s 112-day lockdown 2020.

However, State Opposition Leader Michael O’Brien has been critical of the “apocalyptic” language used to describe the Indian variant, and rejoiced at news of the “false positives”.

“If the basis for the lockdown extension turned out to be false, it should end. Time for the Labor government to be upfront with Victorians,” he tweeted.

-with AAP