International flights into Victoria have been diverted for two weeks as a former judge begins an inquiry into the state's hotel quarantine program.
Since early in the pandemic, thousands of returned overseas travellers have spent a fortnight quarantined in hotel rooms as part of efforts to contain the spread of the coronavirus.
But it has been revealed the program fuelled outbreaks in the city's inner north, prompting Premier Daniel Andrews to send 36 suburbs into lockdown from Thursday.
He said testing indicated a very significant number of cases in late May and early June could be linked to a breach of infection control protocols by staff at these hotels.
"That is unacceptable to me. I'm sure that will be unacceptable certainly to all of those who will be impacted by the restrictions that we have had to reimpose," Mr Andrews said.
The former judge who leads the probe into the operation of the hotel quarantine program will report back in eight to 10 weeks, he said.
In the meantime, the premier has asked Prime Minister Scott Morrison to divert international flights from the state for two weeks.
"I will have conversations with other state leaders to explain that and to thank them in advance of the extra load that they will carry," Mr Andrews said.
There was no detail immediately available on Tuesday night about where the diverted international flights would now land or how the passengers would be processed
Six of the state's 64 new cases on Tuesday were linked to an outbreak among workers at the Stamford Plaza hotel, taking the cluster total to 29.
More than 30 cases have also been linked to the Rydges on Swanston after workers took the virus home, spreading it to their families.
The premier said he was disappointed to hear of breaches of infection control protocols by staff at quarantine hotels, which included instances of members sharing cigarette lighters.
"What might be seemingly innocent, quite low risk, it's not," Mr Andrews said.
"You might never even know that you had it but in the process, you've infected who knows how many people, particularly given if you are from a large family."
The hotel program will restart under the supervision of Corrections Victoria.
On Tuesday, there were 44 international flights scheduled to arrive in Melbourne, including 17 from New Zealand, 10 from China and eight from Qatar.
Opposition health spokeswoman Georgie Crozier said the inquiry into the "scandal-ridden" and "shambolic" program was overdue.
From Thursday, people living in 10 postcodes will return to stage three restrictions.
People in these postcodes will only be able to leave their homes for care or caregiving, to exercise, to purchase food and other essential items, or to go to work or school.
The restrictions will remain in place until at least July 29.
Australian Associated Press
Clarification: As has been subsequently reported, the Victorian government was responsible for the hotel quarantine program, including the contracted security guards referred to by Mr Andrews as "staff members in hotel quarantine". The Stamford Plaza Hotel advises that it did not hire the security workers nor was it responsible for training them, that neither it nor any of its staff breached any infection control protocols and that it has cooperated with the government to conduct testing on all its Melbourne hotel staff, with no positive test results.
