The army has been called in to help contain Victoria's coronavirus outbreak, while authorities are urgently tracking down people who visited five bars and pubs.

Victoria has started its week-long lockdown with four more local coronavirus cases as the military was called on to help monitor thousands of people self-isolating.

Acting Premier James Merlino on Friday confirmed the new cases were linked to the City of Whittlesea cluster, which has grown to 30 since the start of the week.

All have the B1617 strain of the virus, first identified in India, which authorities believe could be 50 per cent more transmissible than other variants.

There are now more than 15,000 primary and secondary contacts who have been told to self-isolate after coming into contact with a COVID-positive case, as well as 150 exposure sites across the state.

Mr Merlino confirmed he has requested Australia Defence Force assistance to check on positive cases and their close contacts to ensure they are staying at home.

"The request will be for around 160 ADF staff for at least the next fortnight to assist our authorised offices in doorknocking positive cases, doorknocking primary close contacts," he told reporters.

"We are effectively doubling our capacity to do that really important work over the next few weeks."

Authorities are also urgently trying to track down people who attended five exposure sites: The Sporting Globe in Mordialloc, Three Monkeys and Somewhere Bar in Prahran, The Local in Port Melbourne, and The Palace Hotel in South Melbourne.

"If you've been to those locations, you've been out partying with somebody who was COVID-positive," the state's head of testing Jeroen Weimar said.

Mr Weimar said one case contracted the virus at The Sporting Globe in Mordialloc on May 23.

It is the first case of community transmission in the outbreak.

"We're very keen to exclude, as quickly as we can, whether there's been any other community transmission at those venues," he said.

A record 47,462 Victorians were tested in the 24 hours to Friday morning, while 17,223 received COVID-19 vaccine dose.

"This is exactly the sort of numbers we want to see each and every day," Mr Merlino said.

Mr Merlino received his first dose of the Pfizer COVID-19 vaccine on Friday afternoon, following the state's decision to open up eligibility to Victorians aged 40 to 49.

He said there was incredible demand for the vaccine within that demographic.

The state's coronavirus hotline was flooded with more than 77,000 calls in 15 minutes when it was announced on Thursday that eligibility would be broadened.

Mr Weimar said 10,000 bookings were confirmed on Thursday, while more than 2000 bookings were made before 9am on Friday.

He urged people to call back later if they were struggling to get through, rather than turning up at mass vaccination centres.

More staff have been assigned to answer calls, while work is underway on an online booking system, Mr Weimar added.

As of 11:59pm on Thursday, Victorians are only allowed to leave home to shop for food and essential items, to provide or receive care, for exercise, work or study, or to get vaccinated.

People must observe a five-kilometre travel limit for exercise and shopping and wear masks both indoors and outdoors.

All non-essential retail is closed, while cafes and restaurants can offer takeaway.

The lockdown is the state's fourth and it is set to end at 11.59pm on June 3.

It is expected to cost Victorian businesses up to $1 billion, with the state government set to announce a support package soon.

Federal Health Minister Greg Hunt ruled out Commonwealth support for affected businesses.

"Victoria is the responsible body. They have said that they will be providing additional support," he told ABC Radio National.

The state opposition said "businesses have been all but forgotten" during lockdown preparations.

There are 39 active cases in total in Victoria, including two new cases in hotel quarantine.