Thousands of Australian Rules football fans were told to self-isolate and get tested for Covid-19 after an infected spectator attended a match in Melbourne and the city raced to avoid another lockdown.
Australia's second biggest city is scrambling to contain a growing Covid outbreak, with 15 cases identified so far, including one who attended the clash between Collingwood and Port Adelaide which drew a crowd of more than 23,000 to the Melbourne Cricket Ground on Sunday.
The AFL said thousands of fans who sat near the positive case were now required to self-isolate until they received a negative test, while health officials were reviewing CCTV to determine if others had also been impacted.
The stadium is one of a growing list of venues across Melbourne visited by positive cases, leaving state health officials rushing to test and trace across the city of five million, which endured a devastating four-month lockdown after an outbreak last year.
AFL games scheduled in Melbourne for the coming weekend are currently allowed to go ahead with fans at up to 85% capacity, but government officials warned public events could yet face fresh restrictions.
"We are concerned about the number and the kind of exposure sites, and the next 24 hours are going to be critical if we are going to have to make any further changes," acting Victoria state premier James Merlino said.
Limits on gatherings were introduced and masks made mandatory indoors yesterday as the virus cluster grew, while New Zealand introduced a temporary pause on its travel bubble with the state.
Victoria reported its biggest single-day rise in Covid-19 cases in more than seven months today and warned the next 24 hours would be critical to limit the spread of a cluster without clamping on tough new curbs.
The six new cases were the largest daily rise since October 2020. Authorities warned that more than 300 close contacts of sufferers had been identified, with many having visited crowded locations.
Other Australian states moved moved to limit movement, with South Australia blocking all arrivals from Victoria.
The cluster has been traced back to an overseas traveller carrying a variant first found in India who had completed quarantine in South Australia, although officials have not worked out how it spread.
The man tested negative in hotel quarantine and flew back to the state capital of Melbourne this month but tested positive six days after he arrived.
Authorities in Victoria believed they had reined in the cluster but an error in tracing the man's movements has caused concern that scores of infections could have gone undetected for a couple of weeks.
Amid growing anxiety, the federal government said it would send 40,000 doses of AstraZeneca's vaccine to Victoria in a scramble to immunise those in nursing homes.
Australia has largely been successful in curbing the spread of the virus, in part through strict border controls that limit flights from overseas and require most travellers to isolate for 14 days on arrival.
But repeated failures of the quarantine system and a sluggish vaccine rollout have prompted critics to attack the conservative government for an apparent reluctance to address the ongoing concerns.
Australia - which has recorded about 30,000 cases and fewer than 1,000 deaths from Covid-19 - has so far administered about 3.7 million vaccination doses in a population of 25 million, but hopes to finish its vaccine rollout by the end of the year.