Preparations for the Australian Open were thrown into chaos Wednesday when up to 600 players and officials were told to isolate and get tested after a hotel staff member tested positive for coronavirus.
Daniel Andrews, premier of Victoria state, said a worker at a hotel the players and officials are staying in became infected with Covid-19.
The man last worked at the Grand Hyatt in Melbourne on January 29 and anyone there was considered a casual contact.
All play on Thursday at five ATP and WTA warm-up tournaments as well as the ATP Cup event featuring the world's top players in Melbourne has been cancelled as a precaution.
"There will be no matches at Melbourne Park on Thursday. An update on the schedule for Friday will be announced later today," the Australian Open said on its Twitter account.
More than 1,000 players, coaches and officials jetted into largely virus-free Australia last month for 14 days' lockdown ahead of the opening Grand Slam of the year.
The Grand Hyatt was one of the designated hotels used.
In a late-night press conference, Andrews said: "There is a number of about 500, 600 people who are players and officials and others who are casual contacts.
"They will be isolating until they get a negative test and that work will be done tomorrow."
But with test results generally returned within 24 hours, he said he did not expect the precautionary move to affect Monday's scheduled start of the Australian Open, the first Grand Slam tournament of the year.
"At this stage, there's no impact to the tournament proper," Andrews told reporters.
The six preparatory tournaments are currently being held at Melbourne Park to get players match fit after their fortnight in quarantine.
While most players were allowed out to train for five-hour blocks during their lockdown, 72 were confined to their hotel rooms 24 hours a day after eight positive Covid-19 cases were detected on the charter flights that brought them to Australia.
Some players only emerged from the strict lockdown over the weekend.
Aggressive restrictions on incoming travel have helped keep the coronavirus at bay in Australia, making it one of the countries still able to have spectators at sports events.
Despite the huge logistical exercise of holding a major tennis tournament during a pandemic, Andrews said sport was not the most important issue.
"I must say that is important to us but the issues are much broader and that is about public health and public safety," he said, but added: "This is one case, there's no need for people to panic."
Health officials said the man was tested at the end of his shift, returning a negative result. He subsequently developed symptoms and was tested again on February 2, with his result coming back positive late Wednesday.
Victoria had gone 28 days without a locally acquired infection. The new case prompted a tightening of rules around mandatory mask wearing and a reduction in the limits of how many visitors are allowed in homes.
Daily crowds of between 25,000 and 30,000 are expected to be allowed to watch the Australian Open, equating to some 390,000 spectators across the two-week spectacle -- around half the attendance of last year.