Travellers from WA who have arrived in NSW in the past week are being told to self-isolate until Friday, after a Perth hotel quarantine security guard tested positive and two million people in WA were put into lockdown on Sunday.
The NSW premier says she's not changing the state's open border policy but all recent arrivals from WA are being screened.
"It is a manageable situation at this stage and there is no reason why we will be altering our border situation," she told reporters on Monday.
NSW Health now requires all new arrivals from WA to confirm whether they attended any of the venues listed on the WA Health website.
Any travellers who have been at places of concern must be tested and self-isolate for 14 days.
"NSW has kicked in to take those reasonable precautions, but we will not be closing our borders," Ms Berejiklian said.
NSW Health had acted quickly with a "proportional response", she said.
"We don't know of any community transmission within WA apart from the security guard, so we are acting according to that risk," Ms Berejiklian said.
Despite longstanding differences with her WA and Queensland counterparts over borders and COVID-19 strategies, Ms Berejiklian insisted "it is not for me to suggest what other premiers should do".
However, she repeated her belief that it was not possible to have an elimination strategy while allowing Australians to return home from overseas because "the disease can leak through the quarantine system and we have to accept that".
"The ... strategy must be zero community transmission and that is what we are working towards," she said.
The key is how you respond to that when there is an outbreak, and that is where obviously the response is paramount.
PERTH COMPLETES FIRST NIGHT OF LOCKDOWN
Swathes of Western Australia have completed their first night of lockdown, triggered after a hotel quarantine security guard attended more than a dozen venues while infected with COVID-19.
From 6pm on Sunday, metropolitan Perth, the Peel region and the South West region entered lockdown, which will last until 6pm on Friday.
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.
Schools which were due to resume on Monday will remain closed for another week.
WA had gone nearly 10 months without a virus case in the WA community before the breach.
Authorities believe the man in his 20s, who worked at the Sheraton Four Points hotel in Perth's CBD, has probably contracted the highly contagious UK variant of the virus and have urged anyone to get tested if they have symptoms.
"I know for many Western Australians this is going to come as a shock," Premier Mark McGowan said.
"Western Australians have done so well for so long, but … this is a very serious situation and each and every one of us has to do everything we personally can to stop the spread in the community."
Mr McGowan said the Maylands man returned a positive test overnight on Saturday after last working at the hotel on January 27. He first experienced symptoms a day after.
He returned three negative tests between January 15 and 23 and it is believed he was probably first infectious from January 26.
The man had worked two 12-hour shifts on January 26 and 27 on the same floor as a person infected with the highly contagious UK variant of the virus.
Genomic testing confirming the source of his infection will not be available until Tuesday morning.
Long queues formed at Perth supermarkets when word spread that a significant announcement would be made. Mr McGowan urged the community not to panic-buy groceries, saying the state was well equipped to ensure supplies.
Other states moved quick to close borders or restrict travel.
South Australia slammed its border shut to all of WA on Sunday night.
Victoria, Queensland, Northern Territory and Tasmania restricted travel from the locked-down areas of WA.