Masks are once again mandatory in all indoor public spaces, except when eating or drinking, and private gatherings have been reduced from 30 to 15.
The plan to increase office capacities to 75 per cent from next week has been delayed and the current cap of 50 per cent will remain in place.
Premier Daniel Andrews urged people not to panic but said acting early would prevent further outbreaks and restrictions down the road.
“We have to assume that this person has infected others,” he said in a late-night press conference on Wednesday.
Mr Andrews also stressed that the case was not a result of any rule breaches and praised the quarantine worker for providing valuable information to contact tracers.
Tennis Australia has not yet said if there will be a knock-on effect for the Australian Open, which is scheduled to begin on Monday, but it will give an update later this morning.
Genomic sequencing is under way to determine how the man contracted the virus and if it is one of the new variants from overseas. The new case comes as authorities investigate how the UK variant spread from one guest to another at the Park Royal Hotel at Melbourne Airport.
