The tennis tournament had been hailed an example of how a 'Zero Covid' approach should work, with as many as 30,000 fans - 50 per cent of capacity - attending matches each day earlier this week.
However, supporters have now been been shut out after 13 cases were found in a quarantine hotel, plunging a population of 6.5 million into lockdown.
The championship was then plunged into further chaos after Greek player Michail Pervolarakis revealed on Instagram he tested positive for coronavirus after travelling from Australia to South Africa.
Ranked 461 in the world, he did not compete in the Australian Open but one week earlier on Friday he played for Greece in the ATP Cup.
Tens of thousands usually flock to Melbourne Park's Garden Square on the first Saturday of the tournament, traditionally one of the most popular days in Australia's sporting calendar, but the venue was left eerily deserted today after the restrictions came into force.
Victorian Premier Daniel Andrews said the five-day lockdown was being enforced to prevent the virus spreading from the state capital.
Only international flights that were already in the air when the lockdown was announced will be allowed to land at Melbourne Airport, schools and many businesses will be closed and residents are ordered to stay at home except to exercise and for essential purposes.
Millions were locked down last night until 11.59pm local time on Wednesday because of a contagious British variant of the virus first detected at a Melbourne Airport hotel that has infected 13 people.
The Australian Open continued without crowds today after Melbourne and the rest of Victoria state went into its third lockdown
Thousands of fans were packed into the John Cain Arena yesterday for a match between Nick Kyrgios and Dominic Thiem
General view of Grand Slam Oval during day six of the 2021 Australian Open at Melbourne Park in Australia this morning
General view outside Rod Laver Arena during day six of the 2021 Australian Open at Melbourne Park this morning
General view of Garden Square outside Rod Laver Arena and Margaret Court Arena during day six of the 2021 Australian Open
Tens of thousands usually flock to Melbourne Park's Garden Square on the first Saturday of the tournament, traditionally one of the most popular days in Australia's sporting calendar, but the venue was left eerily deserted today after the restrictions came into force
The outbreak of 13 cases, which sparked the new state-wide lockdown, started at the Holiday Inn hotel in Melbourne, pictured
Cleaners wearing full PPE disinfect the Holiday Inn Hotel in Melbourne this week after 13 new cases were detected
Nick Kyrgios and Thanasi Kokkinakis of Australia celebrate after winning a point in their Men's Doubles second round match against Lloyd Harris of South Africa and Julian Knowle of Austria
Belgium's Elise Mertens (R) and Switzerland's Belinda Bencic greet each other after their women's singles match
Spectators are seen in the crowd during the second Round Men's singles match between Alex de Minaur of Australia and Pablo Cuevas of Uruguay on Thursday
Spectators in Garden Square watch the Men's Singles third round match between Nick Kyrgios of Australia and Dominic Thiem on Friday
Nick Kyrgios celebrates in front of a packed crowd at Melbourne Park on Friday, before the lockdown was enforced
The championship was then plunged into further chaos after Greek player Michail Pervolarakis revealed on Instagram he tested positive for coronavirus after travelling from Australia to South Africa
Many had rushed to praise Australian authorities when the tournament kicked off earlier this week, describing it as an example for the world to follow.
A local sports reporter said: 'Can't think of a better visual representation of our success, staying safe and living NORMALLY with the virus than a packed crowd in masks. That image will be beamed around the world.'
Others said images from earlier this week showed 'how to make an event like the Australian Open a success during Covid' and said the Australians 'have done so well to get this tournament up and running'.
Mr Andrews said the rate of spread demanded drastic action to avoid a new surge in Melbourne.
He told a press conference: 'The game has changed. This thing is not the 2020 virus. It is very different. It is much faster. It spreads much more easily.
'I am confident that this short, sharp circuit breaker will be effective. We will be able to smother this.'
Melbourne emerged from a 111-day lockdown in October following a fresh wave of infections that peaked at 725 cases a day.
It was largely blamed on lax infection control procedures at two Melbourne hotels where international travellers were required to quarantine for 14 days.
At the time, the rest of Australia was relaxing restrictions due to low case numbers after an initial nationwide lockdown.
Some Australian states have imposed border restrictions on travellers from Melbourne, and federal politicians were on Friday rushing to get to the national capital Canberra to attend Parliament on Monday for fear that the Australian Capital Territory government will restrict their entry.
Prime Minister Scott Morrison and Health Minister Greg Hunt were in Melbourne to inspect biotechnology company CSL Ltd's plant where a local version of the AstraZeneca vaccine is being manufactured.
Mr Morrison said, before the lockdown was announced, that he was confident the state government could handle the cluster.
'I wouldn't be here if I wasn't confident,' he told reporters.
'I've just flown down from Sydney today. That's why I'm here. Business as usual for me being in Melbourne here today.'