Victorian health authorities say they are concerned about transmission of the virus through "fleeting" encounters, off the back of three new locally acquired cases of the virus.

The Health Department on Tuesday confirmed a total of nine locally acquired cases, though six of these were already reported by Acting Premier James Merlino on Monday.

It brings the total number of active cases in the outbreak to 54, all linked to the South Australian hotel quarantine breach.

Two of the three new cases are primary close contacts who were quarantining during their infectious period, and one is considered a 'casual acquisition' and still under investigation.

The case has a "very close proximity" to a known exposure site and authorities are confident they will find a source of the infection.

State testing commander Jeroen Weimar said there had not been any cases outside of Melbourne in the latest wave.

"At this point we have no new exposure site outside greater Melbourne and no positive cases in regional Victoria," he said.

"That is a good thing, but we have a case today we didn't know about yesterday that wasn't a primary close contact.

"This is still an active and dynamic situation, we've seen this morph three or four times in the last few days.

"This is the biggest outbreak we've seen in Australia this year. It is certainly the fastest moving outbreak we've seen anywhere in Australia."

He said there are no mystery cases.

Health Minister Martin Foley would not be drawn on whether a 'ring of steel' would be implemented separating metropolitan Melbourne from the regions.

"It all depends on what the recommendations from the Chief Health Officer and public health team are," he said.

"The public health team are currently going through all of that data. We've still got, particularly at Axedale and Cohuna, a number of people in quarantine.

"They might well turn positive. Let's hope not, but so far so good.

"The Chief Health Officer and public health team will make recommendations based on all the most up-to-date intelligence and material available.

"As soon as the recommendation is made, as soon as that goes to the processes, we will be talking to the people of Victoria about what the next stages are, but at the moment it continues to be a day-by-day case proposition.

"This is a significant and very concerning outbreak."

Some 42,699 Victorians were tested in the 24 hours to Tuesday morning, while 20,484 were vaccinated.

There are now more than 300 exposure sites linked to the outbreak and 4000 close contacts self-isolating, of which about 75 per cent have returned negative tests.

Of greatest concern to authorities are three cases linked to an aged care facility in Melbourne's northwest.

Two workers at Arcare Maidstone and a 99-year-old resident have tested positive for COVID-19, prompting the federal government to scramble to complete vaccinations in aged care facilities.

It was revealed on Monday the resident, who has been taken to hospital for treatment, received just one dose of the Pfizer vaccine.

One of the workers also received a dose but the other, who also worked shifts at BlueCross Western Gardens in Sunshine from Wednesday to Friday, has not.

There were no additional cases at Arcare Maidstone or BlueCross reported today.

All staff and residents at BlueCross have tested negative other than that one case reported yesterday, which was the crossover worker between Arcare and BlueCross.

Minister for Disability, Ageing and Carers Luke Donnellan announced a five-day vaccine blitz to ensure workers in the vulnerable settings are protected.

From Wednesday June 2 to Sunday June 6 workers in private aged care facilities and the residential disability sector, which are managed by the Commonwealth, will be given priority access at walk-in vaccination hubs between 9am and 4pm.

"This is very much a call to arms of those workers on the frontline to come out and we will give you a priority lane so it makes it quicker and easier to get through it in a speedier time," he said.

"We very much want to ensure we are protecting those vulnerable people in aged care facilities and disability sector from COVID-19."

Mr Weimar urged eligible people to get vaccinated.

"Vaccinations are the only way out of this," he said.

"The vaccine you get will be the same as anybody else; if you are under 50 you will have Pfizer, if you're 50 or above you will have AstraZeneca.

"If you are standing in a queue right now, the queues are running at about two to three hours, my thanks to you for doing so.

"Anybody who wants access to Pfizer if you are 40-49 please contact our call centre, please be willing to be patient, please be willing to try a number of times.

"20,000 people got through yesterday, and a similar number will get through today."

He said the outbreak is different to previous ones experienced in Victoria.

"We are concerned about four or five instances we have now seen where we have seen transmission with very fleeting contact," he said.

"There is evidence of casual acquisition instead of those in direct close contact like friends at a pub or family members."

Earlier, 9am:

Federal MP Bill Shorten, whose electorate of Maribyrnong takes in the Maidstone facility, said workers in both the public and private systems should have been vaccinated by now.

"It is disgraceful that residents and aged-care workers and the same with people with severe disabilities and disability workers have not yet been vaccinated," Mr Shorten told Nine Network on Tuesday.

"The anxiety on people is shocking."

More than three months into the vaccine rollout, 75 per cent of the nation's aged care facilities have had second dose visits, though in Victoria 36 per cent are still waiting for second doses.

"Everybody would have liked to have done it faster but logistically, we've done it as quickly as we possibly could," federal Aged Care Services Minister Richard Colbeck told ABC Radio National.

He conceded he did not know how many staff had received the jab.

"We don't have the consolidated data," Senator Colbeck said.

National cabinet will on Friday consider a proposal to make vaccination mandatory for all aged and disability care workers.

Meanwhile, contact tracers are yet to determine how the first aged care worker caught the virus, with a genomic sequencing report expected to be finalised as early as Tuesday.

When asked if the lockdown could be extended beyond 11:59pm on Thursday, Acting Premier James Merlino said the outbreak could get "worse before it gets better".

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Victoria's Chief Health Officer Brett Sutton said authorities were "neck and neck" in the fight against the virus.

"It's been a rapidly moving virus and the transmission that's occurred in those high-risk settings has been very substantial, so we have to take it as a day-by- day prospect," he said on Monday.

Professor Sutton would not rule out a return of the "ring of steel", a series of road border checkpoints that separated Melbourne and regional Victoria during the state's second wave of COVID-19 last year.

But the police union has come out against such a move, describing it as ineffective and inefficient.

"We think there's a better way of doing it," Police Association Secretary Wayne Gatt told ABC Radio Melbourne.

Two new cases of COVID-19 were also recorded in hotel quarantine on Tuesday.

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