Authorities say there is evidence of “stranger to stranger” virus transmission in Victoria’s latest COVID outbreak – with even fleeting contact enough to pass on the deadly virus.

The outbreak that has locked down the state this week grew to 54 cases on Tuesday.

COVID-19 testing commander Jeroen Weimar said at least four involved transmission between people who were unknown to each other.

“This is stranger to stranger transmission,” Mr Wiemar said.

“What we’re seeing now is people are brushing past each other in a small shop, they are going to display home, they are looking at photos in a Telstra shop.”

“This is relatively speaking, relatively fleeting. They do not know each other’s lives, and that is very different from what we have been before.”

“This is certainly the fastest moving outbreak we’ve seen anywhere in Australia. For a long time. I’m not taking this lightly,” he said.

The state confirmed nine new locally acquired infections overnight, but that tally included six reported on Monday.

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Health Minister Martin Foley confirmed two of the three new cases were identified as close contacts of existing patients and had been in self-isolation.

However, one – which remains under investigation – is not a close contact and has not been linked to an exposure site.

“They are not a known contact and are not directly linked to any exposure site but there is very close proximity to that exposure site and we are confident that the investigation that’s ongoing will uncover further crossover points,” Mr Foley said.

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Mr Foley said the outbreak, which originated in hotel quarantine in South Australia, is “playing out a bit differently to earlier outbreaks”.

“There is evidence of casual acquisition instead of those in direct close contact, like friends at a pub, family members,” he said.

Mr Weimar urged anyone who visited busy shopping centres listed as exposure sites, including Craigieburn Central Pacific Epping, Epping North shopping centre and Broadway Reservoir, to get tested.

He said there was possible exposure at Bay Street shopping strip in Port Melbourne and Clarendon Street in South Melbourne.

There are more than 300 exposure sites across Victoria and 4800 primary close contacts linked to the outbreak. Of those, 75 per cent have returned negative tests.

There were no new exposure sites outside Melbourne on Tuesday morning.

• See a full, and updated, list of sites here

Mr Foley said it was “too early to predict” whether Victoria’s lockdown would end as scheduled at midnight on Thursday.

No decision has yet been made to extend the seven-day shutdown.

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

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

Vaccine blitz for aged care, disability workers

In other developments on Tuesday, Victoria will launch a blitz to get as many aged care and disability workers vaccinated as possible by the weekend.

Minister for Disability, Ageing and Carers Luke Donnellan said workers would be allowed to jump lengthy queues at 10 of the state’s hubs to get shots of Pfizer or AstraZeneca vaccines.

“We’ll undertake a five-day vaccine blitz to ensure workers in the vulnerable settings are protected,”  he said. 

Express lanes will be opened for aged care and disability workers from Wednesday at centres include the Royal Exhibition Building, the Melbourne Convention and Exhibition Centre, Sandown Racecourse, the Melbourne Showgrounds, Geelong’s former Ford factory and others in regional Victoria. They will operate from 9am to 4pm and workers will need to show proof of employment.

“We will keep doing all we can to ensure we are making it as easy and as fast as possible for healthcare and aged care workers in the public or private sector to get vaccinated as quickly as they can,” Mr Foley said.

Workers can also go to any of the state’s other vaccination centres to get doses, but will have to join walk-up queues.

The announcement of the blitz came as it was revealed that less than 10 per cent of aged-care staff across Australia have been vaccinated through federal government visits to nursing homes.

Just 57 per cent of aged-care residents in Victoria and 64 per cent nationwide have received both doses more than three months after the rollout began.

Progress is even slower for people living in disability care with just 355 – or about 1.6 per cent – of more than 22,000 residents receiving both doses.

Aged care and disability are in the highest priority category, which was due to be completed six weeks into the 110-day-old rollout.

Victoria’s outbreak has already spread to aged-care homes in Melbourne at the weekend. Two workers and a 99-year-old resident at Acare’s Maidstone home, in Melbourne’s inner-north-west, have been confirmed with the virus.

The resident, who in hospital, had had just one dose of the Pfizer vaccine.

One of the workers also received a dose. The other, who also worked at BlueCross Western Gardens in Sunshine last week, has had none.

Both facilities have been locked down as all staff and residents are tested.

Mr Weimar said 146 tests had been done at Arcare Maidstone, with only the three confirmed positives. All staff and residents at the BlueCross home have also been tested, and all tests so far are negative.

-with AAP