South Australian authorities say they are facing a “dangerous situation” after reporting 17 coronavirus cases in the state’s first outbreak since April.
The cluster is thought to have spread from a worker at a hotel quarantine site in Adelaide to infect a large local family, officials said.
The state has closed schools and shops and ramped up contact tracing.
Australia had seen cases drop to near zero after beating its second wave in Victoria.
That state’s capital city, Melbourne, had been the centre of a massive outbreak which caused more than 20,300 cases and 800 deaths.
The city spent almost four months in a stringent lockdown before re-opening last month.
Victoria’s outbreak also originated from a hotel quarantine site.
“It’s obvious that the highest risk in Australia right now is this risk of [virus] importation in our quarantine hotels,” South Australia’s chief health officer Nicola Spurrier said on Monday.
She confirmed one infected person had been working at a quarantine hotel and “this is where we are considering the source to be”.
Australia closed its borders to international travellers in March but has allowed citizens and permanent residents to return home if they undergo a mandatory 14-day quarantine in a hotel.
About one-fifth of the country’s cases have been found in returning travellers.
‘Time is of the essence’
State Premier Stephen Marshall urged locals with any symptoms to get tested for the virus, saying time was “of the essence”. Authorities set up pop-up clinics on Monday.
In response to the outbreak, Western Australia, Tasmania and the Northern Territory reinstated quarantine requirements on South Australian travellers.
Australia is widely seen to have handled the virus successfully through strict travel restrictions and an aggressive testing and tracing regime.
Despite health system mistakes which saw the virus gain hold in Melbourne, the city has now seen 15 consecutive days of zero cases following its lockdown.
Australia has about 90 active cases. It has recorded 907 deaths and 27,725 cases so far.