"To put that in some perspective, the usual transmission is about five to six days - In some of these cases, within a day it's been transmitted".
The additions bring the number of people in Victoria's latest cluster to 26.
The number of positive Covid-19 case numbers in Melbourne continues to rise and was at 34 this afternoon, according to Health Victoria.
In response to the Victorian outbreak, South Australia will not allow people to cross the border if they have been in Melbourne, except for its residents and essential workers.
Most of those cases are linked to a man in his 60s who fell sick on May 17.
"Unless something drastic happens, this will become increasingly uncontrollable".
"The vaccine rollout has been slower than we have hoped", he said. "But sadly we are not".
Victoria last entered a five-day "circuit breaker" lockdown in February, when the virus escaped hotel quarantine and infected 13 people.
Supermarkets, food stores, petrol stations, pharmacies, bottle shops and banks will remain open.
Childcare and kinder will stay open, but schools will close. Those in Greater Melbourne must wear a face mask indoors.
All New Zealanders who have returned form Melbourne since May 11 have been provided advice to check locations of interest in Melbourne.
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There was no official word on how many may have been killed amid the scramble to flee the city late Saturday. Power was already cut in large parts of the city when hundreds of residents began leaving their homes.
Merlino said that the person in ICU was "not in a good way".
One of the 12 community cases recorded in the 24 hours to midnight was announced at yesterday's press conference.
Permitted travel must only occur within a five-kilometre radius of a person's place of residence and shopping will be limited to one person per household, per day.
NSW is asking any Melbourne and Bendigo arrivals to fill out a travel declaration form confirming they have not visited any venues of concern.
Also under pressure over failing to meet initial vaccine delivery targets - with about 3.7 million vaccination doses administered so far in a population of 25 million - the government has pledged additional batches will be sent to Victoria in the coming weeks.
That figure should now increase with Merlino announcing on Thursday that every Victorian aged 40 to 49 would be immediately eligible for the Pfizer vaccine, while those aged over 50 would still be offered the AstraZeneca vaccine.
"If you're eligible, get vaccinated", he said.
National Labor's Opposition health spokesman Mark Butler has blamed the federal government for the breach, despite hotel quarantine being managed by state and territory officials.
'We don't have any intention of closing the borders at this stage, but of course we are very, very concerned with what's going on, ' Ms Berejiklian said.
Prime Minister Scott Morrison batted away the criticisms, saying "no system is foolproof" and pointing to Australia's now low infection and death numbers when compared to other countries around the world.
"There are no certainties, no guarantees, in a global pandemic".