Western Australia's premier is not ruling out delaying the reopening of interstate borders after a Sydney hotel quarantine worker tested positive to COVID-19.
WA is scheduled to open up to NSW and Victoria from December 8, with travellers from those states no longer required to quarantine for 14 days.
But those plans are now under a cloud as WA health authorities seek further information from their NSW counterparts.
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, who appears to have caught public transport while symptomatic, may have been infected through another worker.
"This is why we were very cautious about reopening," Premier Mark McGowan 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.
"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."
Depending on the scale of the outbreak in NSW, WA could also delay reopening its border to Victoria.
The two states are being effectively considered as one jurisdiction by WA health authorities given the flow of travellers.
Mr McGowan said he expected to make a decision over the weekend.
"I realise this is very disruptive to many people and very problematic to many people because they don't know what's happening," he said.
"But at the same time, we have to make decisions that are based upon health advice and based upon the safety of the state.
"The NSW government is confident they have it under control but we want to see and make sure that the evidence supports that before we make a final decision."
The premier said he had contacted NSW counterpart Gladys Berejiklian and offered contact tracing support.
The woman's diagnosis has prompted health authorities to ask scores of people who may have been in contact to "stop and stay".
Travellers from NSW and Victoria have been blocked from entering WA for almost nine months unless they went into quarantine and, until recently, secured exemptions.
Travel from South Australia remains prohibited unless arrivals meet strict exemption criteria and isolate for 14 days.
WA has not had any community transmission of the virus since April.
Australian Associated Press