"This is not the position Victorians wanted to be in but I can't have a situation where in two weeks' time, we look back and wish we had taken these decisions now", Victoria Premier Daniel Andrews told reporters on Saturday.
The harsh restrictions which dominated Melbourne's second-wave lockdown are now in force across the whole state, meaning Victorians can not leave their homes except for the four main reasons of shopping for essential supplies, care and caregiving, limited exercise and essential work.
Australian Open director Craig Tiley gave assurances that the tournament would continue, with players deemed essential workers exempt from lockdown, competing in a "bubble form".
"It's very unusual", said women's world number one Ash Barty, who normally would have had a home crowd of thousands cheering her on, speaking after winning her match on Saturday. "Those essential to the delivery of the event will be on site".
Fans watch the Australian Open at Melbourne Park on Thursday night.
Mr Andrews said the United Kingdom strain of the virus is "so hyper-infectious and moves so fast that it is presenting a very real challenge" for authorities.
Speaking earlier on Friday, Prime Minister Scott Morrison noted hotel quarantine workers have also contracted the virus in Adelaide, Brisbane, Perth and Sydney, sparking short lockdowns in those cities.
"We feel at the moment that the risk is very low", Hunt told reporters.
"This is a significant number of staff we are going through to test to make sure they are safe, and we do that work as swiftly as we can".
Mr Morrison said he understood Melburnians did not want to endure another long lockdown.
The Australian Open tennis Grand Slam announced a ban on fans and said players would be cocooned in biosecure "bubbles" as Victoria state authorities ordered six million people into lockdown on Friday to stamp out a new coronavirus outbreak.
"As other states have demonstrated, you can get on top of this pretty quickly, and I have reason for confidence that they can do the same thing by following that same process", he said.
Health officials and the Australian Open's chief said they were not concerned about a tennis player, Michail Pervolarakis, who tested positive in South Africa after returning from a tournament in Australia.
One of the five is believed to have had some contact with Camberwell Grammar School.
The two new cases have prompted authorities to add a Woolworths, bakery and two swimming centres to its growing list of exposure sites. Nonetheless, it is a blow to the tournament, which had been operating with a limit of 30,000 fans per day, organised around three zones to ensure that social distancing regulations were followed.
"We're now a year down the track and we should be thinking of other ways of handling this".
The problems at the Australian Open, the biggest worldwide sports event so far this year, underline the difficulties of holding the much more complex Tokyo Olympics, which are due to start in July after a year's delay.