Victoria has recorded 29 new locally acquired COVID-19 cases, all linked to current outbreaks but not in quarantine while infectious.
The state's Delta variant outbreak has also spread to a public housing tower in the Melbourne suburb of Flemington previously placed under strict lockdown in early July.
Saturday's case count, from 43,618 test results, follows a tally of six infections reported on Friday and with the state now managing 95 active cases. Victorian facilities administered 22,600 vaccine doses in the 24 hours to Friday evening.
Premier Daniel Andrews said it was "a certainty that there are more cases out there".
"We have mystery cases, at least two," he told reporters.
"We don't know where they are, who they've given it to, and everyone is at risk."
The growth of the current outbreak aside, the premier said it was still too soon to tell whether the state's week-long lockdown could be lifted on Thursday.
He said the escalation in cases meant getting tested was now "absolutely critical".
"It is non-negotiable, cannot wait one hour, cannot wait one afternoon," he said.
"It is very significant to see this many cases. Although they are rolling, they are linked to outbreaks and we don't know where those two outbreaks started so they are mystery cases that sit behind this."
Mr Andrews said he could not be prouder of the sacrifices Victorians had made during the course of five previous lockdowns.
"We have it in us to continue to do this work, as tough and hard and gruelling as it is," he said.
"As much as we would love this to be over, none of us have the luxury of pretending it is."
More than 10,000 close contacts of positive cases in the state are currently isolating with 82 venues listed as exposure sites.
Among them is the residential tower at 130 Racecourse Road, Flemington, which has been identified as a tier 2 location between 3 and 6 August.
COVID-19 Commander Jeroen Weimar said eight cases were in a single-family within the building, who were now in quarantine.
"All other residents of the building, we will also provide additional testing capacity for," he said.
"There's a dedicated testing centre being set up on site as we speak. Other residents of the building on the other floors will progressively be asked to go into the centre to get tested over the course of today and tomorrow."
State ombudsman Deborah Glass determined a decision to place nine public housing towers in North Melbourne and Flemington into immediate hard lockdown on 4 July
Other tier one sites listed overnight included a medical centre and a pathology collection centre, both in Caroline Springs.
Several schools were also added as tier two sites, including Heathdale Christian College in Werribee and Warringa Park School in Hoppers Crossing, after positive cases were found in students.
Al-Taqwa College, the centre of an outbreak during Victoria's second wave, has also reported several staff and student cases.
"We are working with those who have tested positive to ensure they and their families are supported and have access to the help and services they need while they isolate and recover," it said in a statement.
Although declining to providing details, the premier said the federal government had agreed to soon supply the state with an additional 150,000 Pfizer doses.
A teacher from Melbourne's Al-Taqwa College has tested positive to COVID-19. Source: AAP
Victoria's seven-day lockdown began at 8pm on Thursday, with the stay-home rules applied during last month's lockdown reimposed.
