Victoria will begin a seven-day lockdown in an effort to contain a rapidly spreading COVID-19 outbreak in Melbourne's northern suburbs, which has now grown to 26 cases.
Acting Premier James Merlino confirmed the lockdown will begin at 11.59pm on Thursday after the state recorded 11 new cases linked to the City of Whittlesea outbreak overnight.
People will only be able to leave home for five reasons - to shop for food and essential items, provide or receive care, exercise, work or study if they are unable to from home, and to get vaccinated.
A five-kilometre travel limit will also be imposed 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, with shopping limited to one person per day, per household.
Cafes and restaurants will only be able to offer takeaway.
Childcare and kinder will stay open but schools will close, except for a small cohort of students.
The lockdown is set to end at 11.59pm on June 3, though Mr Merlino said it could end earlier.
He said he had faith in the state's contact tracing team but the virus was "running faster than we have ever recorded".
There are now more than 10,000 primary and secondary contacts of positive cases as well as 150 exposure sites, including the MCG, Marvel Stadium and bars in Prahran and South Yarra.
"Unless something drastic happens, this will become increasingly uncontrollable," Mr Merlino said.
He also revealed one of the 26 cases - a person aged in their 70s - had been placed on a ventilator in intensive care.
The patient, who hadn't been vaccinated despite being eligible, is now out of ICU but remains in hospital.
Chief Health Officer Brett Sutton said it was "absurd" to suggest contact tracing was failing.
He said it was "reassuring" the 26 cases are linked, but warned all have the Indian B1.617.1 variant of the virus, which is spreading "rapidly".
"One infected individual on average infects five others, so that's five, 25, 125, 625 (cases) in four generations. You do not want this to move unmitigated," Professor Sutton said.
The Indian strain can take one day to infect another person compared with earlier strains which took about five or six days, Mr Merlino added.
He blamed the federal government for the lockdown, saying they have failed to vaccinate enough of the population or set up safe alternatives to hotel quarantine.
Genomic sequencing shows the outbreak is linked to the case of a Wollert man, who caught the virus in South Australian hotel quarantine.
But a definitive link between the Wollert man and the Whittlesea outbreak has not been established.
Mr Merlino acknowledged the cost of the lockdown to businesses and event organisers, adding there would be announcements "in coming days" about support.
"We need to have this circuit breaker lockdown, we know that it works, we know that it makes a difference. We've done this before. Victorians know what to do," he said.
The lockdown is Victoria's fourth.
The state's last was the five-day lockdown in February when the UK strain of the virus escaped hotel quarantine and infected more than a dozen people.
The second lockdown during 2020 was the nation's longest at 112 days.
Opposition Leader Michael O'Brien said now was not the time for politics.
"My message to Victorians is we can do this because we've done it before. This is our fourth lockdown, we know the drill," he said.
There are now 34 active cases in total in Victoria, including cases in hotel quarantine, with more than 40,411 tests in the 24 hours to midnight Wednesday.
Some 12,677 vaccine doses were administered during the same period.
From Friday, the state's vaccine program will expand, with people over 40 eligible for the Pfizer jab.