The entire state of Victoria will be plunged into a lockdown from midnight as the state government frantically tries to curtail the spread of its alarming Covid-19 outbreak.
Acting Premier James Merlino announced the Stage Three restrictions will last for seven days.
"Unless something changes, this will be increasingly uncontrollable," he told reporters.
Residents will only be allowed to leave their homes for five essential reasons, those being work or education, essential shopping, two-hour exercise, medical treatment or assistance and to get vaccinated.
Shopping and exercise can only take place five kilometres from a resident’s home while pubs, cafes and restaurants will only be allowed to provide takeaway services.
Visits to aged care and health facilities will be prohibited unless meeting the exemption criteria.
Masks will now be compulsory as outside as well as in public indoor locations.
Childcare and kinder will stay open, but schools will close.
Visitors to homes are not allowed unless intimate partners.
Virus spreading 'faster than ever'
Mr Merlino said the state's public health experts' "primary concern is how fast this variant is moving".
"We've seen more evidence we're dealing with a highly infectious strain of the virus, a variant of concern, which is running faster than we have ever recorded," he said.
He said the speed at which the virus was being contracted and passed on was now far quicker, with the onset of symptoms now between one to two days as opposed to about five days previously.
Chief Health Officer Brett Sutton said the strain, which is the Indian B1617 variant, "really is rapid and that's led to the exponential increase".
Mr Merlino said more than 10,000 primary and secondary contacts have been identified alongside more than 150 exposure sites which stretch from the NSW border to the Mornington Peninsula.
All contacts are required to isolate.
He confirmed the 11 new cases were linked to previous cases. One of the cases is in ICU and requires a ventilator.
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 has not been established.
Acting premier pleads for Victorians to get vaccinated
Mr Merlino also announced the state's vaccine program will expand, with people over 40 now eligible for the Pfizer jab. He stressed how vital it was that Victorians came forward for the jab.
"The only way through this pandemic is everyone getting vaccinated as quickly as you are eligible," he said.
The lockdown is Victoria's fourth.
Professor Sutton hit out at suggestion the state's contact tracing system was failing.
"That is absurd.. it is an absurd proposition that contact tracing has gone wrong. We have talked about exactly what the contact tracing team have done here and it is extraordinary," he said.
In the wake of the outbreak, WA has imposed a hard border with Victoria, following the lead of South Australia which blocked those from Greater Melbourne.
Tasmania will implement similar measures for Victoria from 2pm. The Northern Territory will force Greater Melbourne and Bendigo arrivals into quarantine.
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