Travellers from Western Australia who have arrived in NSW in the past week need to self-isolate until Friday.
NSW Health says those who have arrived since January 25 are now subject to the same 'stay-at-home' restrictions they would have faced if they had remained in WA.
From 6pm on Sunday metropolitan Perth, the Peel region and the South West region went into lockdown, which will last until 6pm on Friday.
The lockdown was triggered after a hotel quarantine security guard attended more than a dozen venues while infected with COVID-19.
Passengers who arrived in Sydney on a flight from Perth on Sunday night were screened for symptoms of COVID-19, and asked if they had been to any venues of concern identified by WA Health.
None of the passengers reported being at any of those sites.
The new Public Health Order requires all new arrivals in NSW to complete an interstate traveller declaration confirming whether they attended any of the venues listed on the WA Health website, and providing contact details.
Any travellers who have been at places of concern will be required to be tested and isolate for 14 days.
The new infection came after WA had gone nearly 10 months without any local COVID-19.
All residents must stay at home unless shopping for essentials, attending to medical or healthcare needs, exercising within their neighbourhood or working if unable to do so remotely.
Meanwhile, travellers from all parts of NSW can now enter Queensland after the Sunshine State dropped its border restrictions.
Queensland closed the border to 35 local government areas in Greater Sydney, Wollongong and the Central Coast in the midst of December's COVID-19 outbreak, causing chaos for festive season travellers.
But with NSW recording more than 14 days without a local virus case, Queensland's border checkpoints are being dismantled from Monday.
Queensland has barred NSW residents from entering the state three separate times since the pandemic began.
Premier Annastacia Palaszczuk's announcement was warmly received south of the border. However her plea for an extension of JobKeeper to aid the tourism industry was not.
NSW Premier Gladys Berejikilian said the Queensland leader had created some of the tourism sector's hardship, through "hasty" border decisions.
"(Ms Palaszczuk) is now the victim of a policy she put in place herself," Ms Berejiklian said.
NSW Treasurer Dominic Perrottet also took a swipe, saying Ms Palaszczuk needed to realise "money doesn't grow on banana trees".
The Queensland premier dismissed the criticism, saying outsiders can call her whatever names they want "but honestly, I will always stand up for people in this state".
She said tourism operators in the far north of the state, in particular, had told her the main problem was not the domestic downturn but a lack of international visitors.
Border restrictions imposed on Greater Sydney by the ACT and Victoria relaxed on Friday, while Tasmania and South Australia eased their restrictions on Sunday.
Australian Associated Press
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