Acting Premier James Merlino confirmed the state will enter the "circuit breaker" lockdown at midnight on Thursday.
"Unless something changes, this will be increasingly uncontrollable," he told reporters.
He added the spread of the outbreak was causing great concern, with more than 10,000 primary and secondary contacts.
People will only be able to leave home to shop for food and essential items, provide or receive care, exercise and to work or study if they can't from home, and to get vaccinated.
The 5km travel limit will also be reimposed for exercise and shopping, as will compulsory use of masks both indoors and outdoors.
All non-essential retail will close but essential stores like supermarkets, bottle shops and pharmacies will remain open. Cafes and restaurants will only be able to offer take-away. Childcare and kinder will stay open, but schools will close.
There are now 79 exposure sites across Melbourne and regional Victoria, including the MCG and Marvel Stadium. There were infected people at AFL matches at the weekend, while another visited three bars in Prahran and South Yarra, which is of concern to authorities.
Genomic sequencing shows the outbreak is linked to the case of a Wollert man, with an official SA report on Wednesday suggesting he caught the virus from aerosol transmission in an Adelaide quarantine hotel. But a definitive link between the Wollert man and the Whittlesea outbreak hasn't been established.
There are now 34 active cases in total in Victoria, including cases in hotel quarantine, with more than 40,411 tests conducted in the 24 hours to midnight Wednesday.
Some 12,677 vaccine doses were administered during the same period.
The lockdown is Victoria's fourth. The state last was the five-day "circuit breaker" lockdown in February when the virus escaped hotel quarantine and infected more than a dozen people. The second lockdown was during 2020 and lasted 112 days.
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