NSW residents may be locked out of Western Australia for longer, after a Sydney hotel quarantine worker was diagnosed with COVID-19 just days before the border is due to open.
Thousands of travellers from Victoria and NSW, many of whom had not seen family and friends in WA since April, rushed to book flights home for the festive season after it was announced the border would lift on December 8.
Now, just five days out, WA Premier Mark McGowan has refused to rule out delaying reopening the border, citing concern a cluster could form from the new NSW case.
"We don't have enough information at this point in time to make that decision but we expect to get more information over coming days," he told reporters on Thursday.
"Obviously if the chief health officer recommends that we delay opening to NSW, then that is the decision we will make."
However, Queensland authorities have said its state borders would remain open for now after travel restrictions were lifted on Tuesday.
"The government is keeping a close eye on what is happening in Sydney and our health experts are in regular contact with their NSW counterparts," Health Minister Yvette D'ath told the Queensland parliament.
The new case, a woman who works at one of the Sydney quarantine hotels, ends the state's 26-day streak without a single new case of COVID-19 in the community.
The woman's diagnosis has prompted health authorities to ask scores of people who may have been in contact to "stop and stay".
Anyone who worked with the woman or caught the same train between Minto and Darling Harbour is being asked to get tested and isolate until they hear from health authorities.
"It's sort of a hold and stay until we've assessed the extent of what is going on," Chief Health Officer Kerry Chant told reporters on Thursday.
Urgent genomic testing is under way to determine how the woman contracted the virus, with results due within 48 hours.
Authorities are concerned the woman may have been infected through another worker.
"She didn't have contact with infected overseas quarantine patients directly ... so at the moment, there isn't a smoking gun in terms of how we would say the transmission event happened," she said.
The woman, who performed house duties at the Novotel and the Ibis at Darling Harbour, was diagnosed late on Wednesday.
Her five household members have since returned negative tests, and NSW Health is awaiting the test results of a small number of her close contacts.
As a precaution, NSW Health is also conducting wider testing of staff at the hotel complex.
Breaches of hotel quarantine are bound to happen, Ms Berejiklian says, with the state due to welcome back its 100,000th returned traveller within days.
"This is a real test for NSW, but I'm confident if we continue the path we're on, that we will pass this test yet again."
Prime Minister Scott Morrison also said he had great confidence NSW could contain any outbreak.
"They are the gold standard not just in this country but anywhere around the world," he told reporters.
The case comes a day after Ms Berejiklian announced a swathe of social restrictions would be eased from Monday.
There were no plans to rescind the relaxed measures at this stage.
Meanwhile, NSW Health is calling on people in Sydney's northwest to get tested after traces of the virus were detected at a sewage treatment plant in Riverstone.
Fragments of the virus were detected in samples taken on Sunday from the sewerage system that drains parts of Riverstone, Vineyard, Marsden Park, Shanes Park, Quakers Hill, Oakville, Box Hill, The Ponds, Rouse Hill, Nelson, Schofields and Colebee.
Australian Associated Press