Acting Premier James Merlino has announced that from 6pm AEST on Tuesday private home gatherings in metropolitan Melbourne would be limited to five people per day, public gatherings to 30 people, and everyone aged 12 years and older would need to wear face masks indoors, unless an exemption applies.
Mr Merlino said the new restrictions were based on public health advice.
“This is about giving our contact tracers the time they need to track this matter down and get on top of it,” he told reporters.
Under the revised restrictions - in place until at least 4 June - schools, workplaces, bars, cafes and restaurants can stay open.
People who live in metropolitan Melbourne can still travel to regional Victoria - however the rules will accompany them when they leave the city, meaning they will still need to wear a mask indoors and the person they visit will only be allowed five visitors to their house that day.
Revised mask and gathering restrictions in Melbourne
Ticket sales for this weekend's AFL matches in Melbourne have been put on hold.
New Zealand has also announced it is pausing the travel bubble with Victoria for 72 hours from 6pm AEST Tuesday.
Authorities have identified more exposure sites in Melbourne, which can be found on the state government’s website, and expect the list to grow in the coming days.
The Whittlesea cluster first emerged on Monday.
Genomic sequencing has found the outbreak is linked to the case of a man from Wollert, located in the area, who contracted the virus in South Australian quarantine earlier this month.
But Victoria's Chief Health Officer Brett Sutton said on Tuesday morning authorities were yet to establish a "definitive link" between the Wollert man and the Whittlesea cases.
"There may still be another intermediary. We need to explore that, but we need to finish the very lengthy, very detailed interview with that case this morning," he said.
Professor Sutton confirmed the COVID-19 variant in the Whittlesea outbreak is B1617, which was first identified in India in October last year.
"We shouldn't be complacent about this variant. It is at least as infectious as the so-called UK or Canterbury [variant]," he said.
Professor Sutton on Monday urged everyone to get vaccinated against the virus, something Mr Merlino repeated on Tuesday.
“If you are eligible to be vaccinated, and there are millions of Victorians right now eligible to be vaccinated, do not wait. Get organised today,” he said.
The latest outbreak snapped Victoria's 86-day streak without a locally acquired COVID-19 case.
The operating hours of some 26 testing sites are also set to be expanded, including the Melbourne Showgrounds, which reached capacity after being open for five minutes on Tuesday.