Victoria, the south eastern state in Australia entered a lockdown for the third time in a bid to suppress an outbreak of the UK strain of coronavirus.
At least 13 confirmed cases were traced back to a quarantine worker at a Melbourne Hotel.
The lockdown began on Friday and will end four days later on Wednesday.
The government has allowed the Australian Open tennis tournament in Melbourne to continue. However, spectators would be banned from attending the event from Saturday. Previously 30,000 visitors were allowed a day.
Victorian Premier Daniel Andrews clarified that the current outbreak was not linked to the quarantine hotels used by the tennis players.
He stressed that a “circuit breaker” was needed to combat the “hyper-infectious” strain which he said had likely already seeded other infections in the community.
“This is the fastest-moving, most infectious strain of coronavirus that we have seen,” he said, adding that almost 1,000 close contacts had already been reached.
Prior to this outbreak, Victoria had not seen a local infection for 28 days and the state had largely eliminated the virus.
Many Melbourne residents have expressed dismay but also resignation over the retreat into lockdown again.
Last year, the city endured one of the world’s longest and strictest lockdowns to overcome a second wave of infections which led to over 90% of Australia’s 29,000 cases and 909 deaths.
Meanwhile, South Australia, Queensland and Western Australia have announced travel bans on people from Melbourne. Further border closures are expected. International flights to Melbourne will also be cancelled, authorities said.