West Australian Premier Mark McGowan has welcomed the latest NSW COVID-19 results but says a final call on when to reopen the border won't be made until Monday.
WA is scheduled to open up to NSW and Victoria from next Tuesday, dropping the 14-day quarantine requirement for travel from those states.
The timeline was cast into doubt on Thursday after a Sydney hotel quarantine worker contracted the virus, ending the state's 26-day streak without a single new community case.
But NSW authorities on Friday revealed the woman appeared to have been infected at work, either by a returned overseas traveller or members of a flight crew.
No new local cases were reported in the 24 hours to 8pm on Thursday.
"It is positive news," Mr McGowan told reporters on Friday.
"Obviously there's testing still to be done. The woman in question, the cleaner, spent a lot of time on trains and trams between western Sydney and her workplace and by all accounts was a very gregarious person.
"My expectation is now that we will make a final decision on NSW on Monday so that we take every precaution possible."
The border to Victoria remains on track to reopen on Tuesday, with the premier advised it should not be affected by the NSW outbreak.
Mr McGowan said he would be guided by advice from WA's chief health officer Andy Robertson in making his decision on NSW.
"As you know over the last 12 months, what happens is things change with COVID," he said.
"In the case of Victoria obviously, in the western suburbs of Melbourne, COVID bubbled away undetected for a considerable period of time and then they had that massive outbreak that caused mass deaths and mass disruption.
"So we just want to be cautious, we want to be careful."
Federal cabinet minister Peter Dutton earlier said WA should have faith in the ability of NSW to nail down the source of the infection.
"People can't be forced to cancel their Christmas holidays or reconnecting with family members because of one case," he told Nine's Today Show.
Mr McGowan has spoken to NSW counterpart Gladys Berejiklian to offer support with contact tracing.
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.
"I understand that this is disruptive and causes anxiety for people," Mr McGowan said.
"In coming days, I'm sure NSW will do many thousands of tests. That will provide us with the evidence we need to make a final decision on Monday."
WA has not had any community transmission of the virus since April.
Mr McGowan said more than 260,000 people had downloaded the new SafeWA app with QR code registering to become mandatory from Saturday.
Hospitality venues, gyms, cinemas and other businesses will be required to keep track of patrons or risk fines of up to $250,000.
Australian Associated Press