At a press conference Wednesday morning, Mr Merlino said the next 24 hours would be "critical" in determining further steps to address the evolving coronavirus outbreak.
Victoria recorded 10 new COVID-19 cases on Wednesday, as well as an additional case that will be included in today's numbers.
These new cases are linked to the four initial infections reported on Monday, and all carry the Indian variant of the virus, which is "at least as infectious" as the UK variant.
This came as the coronavirus threat reached northern Victoria, with a COVID-19 case attending a match between the Cohuna Kangas and Tooleybuc-Manangatang on Saturday.
Victorian health authorities said the case attended the Cohuna Recreation Reserve, watching multiple netball games, visiting the canteen inside and using outdoor public toilets.
Anyone who attended the reserve between noon and 5 pm must get tested urgently and isolate until they receive a negative result.
In a statement on the club's Facebook page, the Cohuna Kangas said the Cohuna Complex was closed until further notice and would undergo a deep clean facilitated by the Gannawarra Shire Council.
Two other regional locations have been named as exposure sites, including Bendigo's Hairfolk salon on Saturday morning and the Axedale Tavern at lunchtime Sunday.
More Melbourne exposure sites have also been reported, with authorities announcing late Tuesday a case attended the AFL match between Collingwood and Port Adelaide at the MCG on Sunday.
Anyone who was seated in Zone 4, Level 1, of the Great Southern Stand must get tested and isolate until they receive a negative result.
States and territories have also introduced border restrictions as Melbourne COVID-19 cluster evolves.
Mr Merlino said health authorities were concerned by the "number and kinds" of exposure sites connected to the new cluster.
On Wednesday morning, Chief Health Officer Brett Sutton said the remaining test results from primary close contacts would provide more clarity.
"The exposure sites that they then generate, how many close contacts they might have and how long they have been in the community — they are all factors we need to consider," he said.
Professor Sutton added the hunt continued for the "missing link" between this new cluster and a Wollert man who tested positive on May 11 after completing South Australian hotel quarantine.
Genomic testing has revealed this earlier case and the cluster are closely linked.
New restrictions will be enforced in Greater Melbourne until at least June 4 in response to the growing outbreak.
These include mandatory mask-wearing indoors, a cap on indoor gatherings to five visitors a day and limits on public gatherings to 30 people.
While people can still visit regional Victoria from greater Melbourne, these restrictions will "travel with them".
Asked if the government would make changes to vaccine eligibility in light of the new COVID-19 outbreak, Victorian Health Minister Martin Foley said this was being explored.
"We want people to get vaccinated as soon as possible," he said.
There are currently 23 active cases in the entire state, including people in hotel quarantine.
For a full and updated list of exposure sites, visit coronavirus.vic.gov.au/exposure-sites
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