The Victorian Department of Health said caseloads in Mildura have increased in recent days, with nine active cases in the LGA reported prior to Friday. A further three cases were confirmed on Friday afternoon and will be reported in Saturday’s numbers.
Meanwhile, residents of Moorabool Shire and Greater Shepparton will leave lockdown at midnight on Friday, with restrictions there to match those in place in the remainder of regional Victoria.
Victoria announced on Friday it had recorded 1,838 new locally acquired COVID-19 cases - the highest daily tally of any state or territory since the pandemic began.
There were five further deaths reported in the 24 hours to midnight Thursday, taking the toll from the current outbreak to 75.
Chief Health Officer Brett Sutton also announced Victorian students in years three to six would be required to wear masks indoors when they return to the classroom in an effort to lower COVID-19 transmission.
Professor Sutton said while younger students would not be required to wear masks, it would be "strongly recommended".
"We really want to have these measures in place early on to keep kids in school and to make sure that they are as safe as possible in the school environment," he said.
"It’s just indoors, we know the risk outside is less and we know kids won’t be wearing them running around outside anyway."
Professor Sutton said face masks, along with ventilation and other COVID-safe measures, had prevented transmission in schools overseas.
“We certainly saw in the UK where schools reopened without strong mask use or indeed supported with all those layered mitigations, there was an estimated eight per cent of students absent from school with suspected or confirmed COVID," he said.
Authorities are in the process of drafting the new rules, with a staged return to classrooms in the coming weeks.
Of Victoria's total case numbers, 35 per cent are from the northern suburbs of Melbourne, while 30 per cent are from the west.
The regions account for six per cent of the total cases. Professor Sutton said that from midnight on Friday, the local government areas of Benalla, Bendigo, Buloke, Loddon and Yarriambiack will be added to the state's "border bubble". Some LGAs in NSW including Wagga Wagga will also be added.
There are now 620 Victorian in hospital, including 114 in intensive care, 76 who require ventilation.
Treasurer Tim Pallas said about 66 per cent of patients with COVID-19 in hospital have not been vaccinated, while 26 are partially vaccinated and eight per cent are fully immunised.
About 56 per cent of the state's population aged 16 and over are fully vaccinated, while 84 per cent have had one dose.
Once 70 per cent of the state's population above 16 is fully vaccinated, expected around October 26, Melbourne's curfew will ease, the travel limit will be expanded and venues can open outdoors to the fully vaccinated.
But Victorians will have to wait until the 80 per cent double-dose target is reached, forecast for November 5, for significant changes including Melbourne hospitality reopening for seated service and visitors to be allowed in homes.
Premier Daniel Andrews on Thursday said he had no plans to alter Victoria's roadmap out of lockdown given the high daily case numbers.
With Dijana Damjanovic and AAP.