Australia's second most populous state Victoria entered a five-day lockdown today as authorities raced to prevent a third wave of Covid-19 cases sparked by the highly infections United Kingdom variant.

Andrews se said the latest COVID-19 cases had nothing to do with the tennis quarantine program.

"We've always said the number one priority was the safety of the community and our guests", he added.

American star Serena Williams only learned of the new measures when she came off court after a 7-6 (7/5), 6-2 third-round win over Russia's Anastasia Potapova.

Players also stayed in a "bubble" environment at last year's US Open in NY, which went ahead behind closed doors, and the delayed French Open.

"I didn't know at all until the match was over".

"It's not ideal - it's been really fun now with the crowd back".

Grigor Dimitrov, who also advanced to the fourth round on Friday, said he feels fortunate the tournament is going ahead at all.

The campaign ended on Friday for home hero Nick Kyrgios, who considerably raised the decibel levels at Melbourne Park during his three rounds, before the stands were vacated. The impending lockdown was announced in the middle of her match.

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.

Queensland Acting Chief Health Officer Dr Sonya Bennett said all 1500 people have been asked to quarantine at their place of residence for 14 days, from the time they were last in Greater Melbourne.

Mr Andrews said the "hyper-infectivity" of the United Kingdom variant meant the virus was moving so fast that it presented an enormous risk to the Victorian community.

Authorities are working to track down 5000 people who passed through Melbourne Airport's Terminal 4 after a case worked at Brunetti cafe while infectious on February 10.

From Friday February 12 at 11.59pm, new rules apply to Victoria for five days until 11.59pm on Wednesday February 17 due to a worrying new outbreak of the United Kingdom mutant strain of Covid-19. Most of those were during a second deadly wave past year when a hard lockdown and overnight curfews were put in place in Melbourne.

But spectators, who had been permitted over the first five days in limited numbers, will no longer be allowed from Saturday and players, who are keen to continue, must follow strict new rules.

The lockdown then lasted 111 days.

Meanwhile, no new local coronavirus cases were recorded in NSW for the 27th consecutive day.

In both instances, the outbreak was quickly contained. Several states have announced border closures already for travelers from Victoria.

A sizable number of players were forced into a hard lockdown in their hotel rooms for two weeks because they shared flights with people who tested positive for coronavirus, and there was some grumbling about that, but all in all the tournament was seen as a refreshing step toward normalcy in a sports world that has seen little of it over the past year. That meant 507 people connected to the tournament, including 160 players, had to isolate and get tested for COVID-19.

In a second Instagram post on Saturday, Pervolarakis confirmed he tested negative to COVID-19 the day before he flew out of Melbourne.