A coronavirus outbreak in Melbourne's north has forced some 500 people into quarantine, shut down two schools and left five suburbs on high alert.
But Premier Daniel Andrews insists the state is on track for a further easing of restrictions on Sunday.
Victoria recorded five new cases on Thursday, all linked to the northern suburbs outbreak, and no further deaths.
Authorities had been monitoring the outbreak for a fortnight and considered it contained until a student attended school while infectious.
The grade 5 student attended East Preston Islamic College on Monday and Tuesday before testing positive on Wednesday.
They should have been self-isolating as they were a close contact of a positive case, the premier said.
The school has been closed for deep cleaning, as has the nearby Dallas Brooks Primary School after a close contact was identified there.
The state's Commander of Testing Jeroen Weimar said 73 close contacts at the school, mainly students and some teachers, will quarantine for 14 days along with their households.
"That is a total of around 400 people at this point in time who, under our orders, are primary or secondary contacts and have been asked to isolate for two weeks," he told reporters.
A further 120 people living in a social housing block in Broadmeadows have been told to stay in their apartments for the next 48 hours after a resident tested positive.
"I should stress this is an abundance of caution approach," Mr Weimar said.
"Although we have every reason to believe that the positive case was contained within a particular apartment, we don't want to take any chances."
Some families have been moved into accommodation for the fortnight.
All are being supported by Austin Health, Banyule Community Health and community groups.
The premier said authorities were using the same methods that worked in containing recent outbreaks in Kilmore and Shepparton, in regional Victoria.
"Hundreds of people are locked up at home, that is not pleasant," Mr Andrews said.
"But that approach means that for hundreds of thousands, indeed millions more, there will be a hopefully greater degree of movement."
It's hoped all residents of the housing block will be tested and have their results within the 48-hour timeframe.
A total of 36 people are linked to the northern suburbs cluster, with 16 cases remaining active across six households.
Residents of Broadmeadows, Dallas, Preston, Roxburgh Park and West Heidelberg have been urged to get tested if they experience symptoms.
A community door-knocking program began on Thursday and a text alert was sent to anyone in the area on Wednesday afternoon.
Mr Weimar said the school incident had prompted changes to case management. Rather than dealing with positive cases individually, authorities will now assign a case manager per household.
"That work is starting in some parts of our state and we will accelerate that as we go forward," he said.
Thursday's cases bring Melbourne's 14-day rolling average to 6.1.
The number of mystery cases for the fortnight to October 19 remains at 10.
Despite the likelihood of more positive cases in the northern suburbs, Mr Andrews said the state was well-placed to announce further changes to restrictions on Sunday.
"Every Victorian can be reassured we will only take steps that are safe," he said.
"We've come too far to then lose our nerve as a community and rush to COVID-normal."
The state's death toll remains at 817 and the national figure 905, with only one death in the past week.
There are just five active cases remaining in aged care.
Nine Victorians are battling the virus in hospital, though none are in intensive care.
Australian Associated Press