Acting Premier James Merlino said today the man in his 60s was linked to the City of Whittlesea infection, which now totals five infections.
The other four cases were confirmed on Monday afternoon.
Mr Merlino also announced new restrictions in response to the outbreak to take effect from 6pm today.
Private home gatherings will be limited to five visitors per day, public gatherings will be capped at 30 and face masks must be worn at indoor venues, like shopping centres.
Schools and workplaces will stay open and there are no changes to current density rules.
The acting premier confirmed genomic sequencing showed the Whittlesea outbreak was "closely related" to a man in nearby Wollert who tested positive earlier this month after returning from hotel quarantine in South Australia.
Health authorities have now identified 10 exposure sites as they race to contain the COVID-19 outbreak.
Testing sites serving the city's north were straining 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 B.T. 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 70s and a pre-school aged 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 earlier this month.
More household contacts of the new cases have been put into isolation despite testing negative so far.
Victoria Chief Health Officer Brett Sutton has said the first Whittlesea man is carrying a high viral load and warned the community to brace for more possible cases.
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, Tuesday 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.
