Sydney, Dec 18 : A new coronavirus cluster in Sydney grew to 28 cases on Friday, prompting authorities to reintroduce domestic border restrictions for hotspot areas in the Australian city.
The cluster was reported earlier this week on the city's Northern Beaches, and local residents were asked to stay home for the next three days if possible, reports Xinhua news agency.
Genomic testing revealed the strain of virus originated overseas, most likely in the US.
However, it was not known how it spread into Australia.
New South Wales (NSW) Premier Gladys Berejiklian called on all residents of the state capital to abide by officials' advice, saying she was confident the outbreak could be contained in time for Christmas if protocols were followed.
"We do have the potential to get on top of it, but it does require hard work on the behalf of all of us," Berejiklian said at a briefing here on Friday.
The new cases also prompted other Australian states to tighten their border restrictions, reintroducing mandatory quarantine periods on arrivals from areas deemed high risk.
New restrictions were applied to those travelling from the Northern Beaches to other parts of the country, requiring them to get tested and self-isolate if they had been in the area since December 11.
The State of Western Australia went as far as to expand the requirements to anyone arriving from NSW.
The southern island State of Tasmania withdrew travel exemptions entirely for anyone who had been in the Northern Beaches or in one of several Sydney venues considered potential hotspots.
State leaders said the situation would be monitored closely and more severe restrictions would be considered if the number of cases increased to an unmanageable level.
NSW Health Minister Brad Hazzard said that low virus numbers over the past months had led to an "avalanche" of complacency throughout the community.
"We need to have all of the community aware again that we are in the middle of a worldwide pandemic," Hazzard said.
"There is no room for complacency.
Until we have a vaccine there is no solution."
The state of NSW currently accounts for 4,666 coronavirus cases and 53 deaths.
Australia has so far reported a total 28,072 cases and 908 fatalities.