A hotel quarantine worker and released guest of the same Melbourne quarantine hotel where an infected staff member worked have tested positive for COVID-19.
Health Minister Martin Foley announced the two new cases on Tuesday afternoon, both linked to the Holiday Inn at Melbourne Airport.
The first involves a former resident who returned a positive test after completing her 14-day stay.
The woman, who sought testing after learning of the outbreak, tested negative several times during her quarantine stint before departing the hotel on Sunday.
The returned traveller has indicated to contact tracers she did not leave home, other than to obtain a test.
Only one primary close contact has been identified so far.
Fellow returned travellers on the same floor who left quarantine that day will have to spend another 14 days in isolation.
"We know that this will come as difficult news," Mr Foley told reporters.
"But it is a necessary public health move."
Staff working on the floor face the same routine.
The other case is a food and beverage worker, among the 136 hotel quarantine workers identified as close contacts of an authorised officer who worked at the Holiday Inn.
"It would appear that the person, as a worker at the hotel, has been in the exact same exposure period as this most recent case," Mr Foley said.
Chief Health Officer Brett Sutton said the three cases were likely linked to transmission on the same floor where COVID-positive guests were known to reside.
"It seems to be an issue of picking up the virus during the quarantine period, rather than the virus having a longer incubation period," he said.
No new residents will be placed on that floor and Mr Sutton said the hotel could be completely shut down.
"It'll be a topic for discussion," he said.
"But at the moment it is absolutely focused on that floor.
"If there's any indication that the risk extends beyond that floor, it's an option for us to close the hotel if need be."
It comes as genomic testing confirmed the hotel quarantine worker has the highly-infectious UK strain and authorities separately deal with the state's first intensive care case in four months.
The returned traveller in Victoria's hotel quarantine system has been transferred to intensive care.
According to the Department of Health, the last time Victoria had an active virus case in intensive care was October 10.
Victoria on Tuesday reported no new local or international infections. There are 15 active cases in the state following 12,816 tests.
The Victorian government also plans to ramp up testing for hotel quarantine workers on their days off as a result of the three staff cases.
Mr Andrews expects the new testing rules for workers will be in place by the end of the week, but doubts they will be necessary.
He is confident hotel workers will go for testing on their days off without being told to do so, saying making it mandatory is "a backstop".
"The view of the workforce is that it's a smart thing to do," the premier said.
Opposition Leader Michael O'Brien said the government should have foreseen the need to test workers daily.
"The government was very slack in not anticipating they were going to need to test people, potentially seven days a week," he told reporters on Tuesday.
Mr Andrews said there was no obvious reason for the first Holiday Inn worker's infection, adding there was a "working theory and very significant concerns" about aerosol transmission.
A review of all quarantine hotels' ventilation systems has been initiated, although emergency services minister Lisa Neville doesn't believe it is to blame.
Despite authorities previously carrying out airflow checks before the rebooted program began in December, Mr O'Brien said the government "hadn't done enough".