The five confirmed cases in the Whittlesea outbreak have the Indian variant of the virus, health authorities have confirmed.
Acting Premier James Merlino has announced new restrictions in response to the new outbreak, to take place from 6pm on Tuesday.
Private home gatherings will be limited to five visitors a day, public gatherings will be capped at 30 and face masks must be worn at indoor venues such as shopping centres.
Schools and workplaces will stay open and there are no changes to current density rules.
Mr Merlino said the 30-person rule did not apply to major events but a committee would look at these.
Hospital and aged care visitor restrictions will apply across Victoria.
Mr Merlino on Tuesday morning confirmed the new case, a man in his 60s.
The other four cases in the the Whittlesea outbreak were confirmed on Monday afternoon. The latest infection is a close contact of one of the men who tested positive on Monday.
Chief Health Officer Brett Sutton said the man in his 60s could be the missing link to the man who tested positive in nearby Wollert earlier this month. The Wollert case became positive after returning overseas through South Australian hotel quarantine.
"It may be the missing link ... (but) there may still be another intermediary," Professor Sutton said.
Genomic sequencing has shown the Whittlesea outbreak was "closely related" to the Wollert man.
Prof Sutton said the COVID-19 variant in the Whittlesea outbreak was B1617, which was first identified in India.
"We shouldn't be complacent about this variant. It is at least as infectious as the so-called UK or Canterbury (variant)," he said
Health authorities have now identified 10 exposure sites as they race to contain the Whittlesea outbreak. Testing sites serving the city's north were struggling to cope with demand as people heeded public health advice.
Nando's Epping and Woolworths Epping North joined Jump! Swim Schools Bundoora and Highpoint Shopping Centre as tier one exposure sites in the new outbreak, meaning anyone who attended those places at specified times must be tested and isolate for 14 days.
Futsal Brunswick, Epping North Shopping Centre, House and Party at Epping, Urban Diner Food Court at Pacific Epping Shopping Centre, Shells Coles Express Reservoir and BT Connor Reserve are tier two sites, meaning affected people must get tested and isolate until they have a negative result.
The family cluster - originally involving a man in his 30s, a man in 70s, a woman in her 70s and a preschool-age child from three households in the Whittlesea area - emerged on Monday.
The health department last week admitted it had listed the wrong supermarket as an exposure site when the Wollert man tested positive.
More household contacts of the new cases have been put into isolation despite testing negative so far.
All domestic borders remain open despite most states and territories issuing updated travel advice for recent Victorian arrivals.
The latest outbreak snapped Victoria's 86-day streak without a locally acquired case. Victoria has 14 active cases, with the rest in hotel quarantine, and 14,892 tests in the 24 hours to Tuesday.
Meanwhile, Opposition Leader Michael O'Brien said the public was nervous after the government blundered on the supermarket exposure site and "seems to be making some pretty basic errors" on contact tracing.
"The last thing Victoria can afford is going back into lockdown," he said on Tuesday.
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