Australian health authorities are urgently contacting more than 400 people who arrived from New Zealand last week after Auckland's latest confirmed case of Covid-19.
New South Wales Health has sent out a message to 455 passengers who arrived from New Zealand on or after November 5 - last Thursday.
Everyone who was on a flight was being asked to monitor their health over the next few days and to watch out for symptoms related to Covid-19, ABC News reported.
That message was of particular importance for anyone who had been in the areas where a woman in her 20s, who tested positive for the virus this week, had visited in downtown Auckland.
They include the A-Z Collection store on High St, where the woman worked, the Vincent Residences on Vincent St, where she lives, and the Red Pig Restaurant, where she ate at last Saturday night, from 6pm to 8.30pm.
In a statement, NSW Health said people should look out for even "the mildest" of symptoms and get tested and isolate immediately if they felt unwell.
"They are also required to remain in isolation until receiving a negative result - in line with routine advice for all people in NSW."
Although the warning has gone out, NSW Health also said that the risk posed by quarantine-free travel "remains low" at this time.
Airlines here to refuse anyone who has visited affected locations
Passengers on board a flight that touched down in Sydney - from New Zealand - last night were also given the warning.
ABC said none of the passengers had reported being to any of the venues the latest Covid case had been to. No one was also displaying any flu-like symptoms.
It is understood airlines here would not let anyone on a flight to Australia if they had visited any of the places the infected woman was in the past week or so.
People travelling from New Zealand have been able to fly to parts of Australia - New South Wales and the Northern Territory - under a travel bubble since October 16.
Under the new travel rules, travellers arriving from this side of the Tasman do not have to carry out the mandatory 14-day quarantine period in a managed isolation facility.