UPDATE: Four new cases recorded have been recorded, taking Melbourne cluster to nine.
Acting Premier James Merlino announced the changes, saying they come into effect from 6pm on Tuesday until, at the earliest, June 4.
More details on the new restrictions in the video above
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Masks are mandatory for those over the age of 12 in indoor settings unless an exemption is applicable.
That requirement includes workplaces within Metropolitan Melbourne.
Private in-home gatherings are limited to five visitors per day.
Public outdoor gatherings are restricted to 30 people.
Melburnians are able to travel to regional Victoria.
However, the restrictions in place will travel with them, meaning they must continue to wear masks.
“This is about giving our contact tracers the time they need to track this matter down and get on top of it,” Merlino said.
“Face masks, private and informal gatherings - a reason why we’ve focused in these areas as opposed to businesses and workplaces that will continue under the existing arrangements - it is harder to contact trace in those private and informal settings.”
It comes as a fifth case of COVID-19 is reported.
Four new locally acquired cases were reported on Monday, all from the same family across two households.
A fifth case, a close contact, was notified by the Department of Health after midnight.