NSW has extended by a week the stay-at-home order for people who have arrived from Victoria, after the southern state lengthened its lockdown.
Anyone in NSW who has been in Victoria after 4pm on Thursday May 27 will have to stay at home until June 10.
NSW Health will review the measures then, it said in an alert issued on Thursday afternoon.
No local cases of COVID-19 were detected in NSW after more than 18,000 people were tested following a scare on the south coast.
NSW Health on Wednesday night issued alerts for several possible COVID-19 exposure sites inland at Gundagai and Goulburn, and more on the coast at Jervis Bay, Huskisson and Vincentia.
The venues were visited last month by a Melbourne family of four who were later diagnosed with COVID-19.
There were fears the virus had infiltrated NSW after the father had symptoms on May 25 after driving back to Melbourne on May 24.
He tested positive on Monday, nearly a week later, as did his wife and children.
NSW Health ramped up testing in the area, with several pop-up clinics, but no new cases were detected in the 24 hours to 8pm on Wednesday from 18,672 tests.
Two new overseas-acquired cases were recorded in the same period.
Chief Health Officer Kerry Chant said NSW Health was working with Victorian authorities to determine who in the family contracted the virus first.
"If this gentleman was the source for those individuals, then they were not potentially infectious when they were in NSW, and clearly if the reverse is the case that may take back the exposure period," she told reporters on Wednesday.
Already 243 people have been instructed to get tested and isolate while they await further instructions from NSW Health.
"We've asked (them) to stop and stay until we actually really understand and do a full assessment of the risk," Dr Chant said.
Victorian authorities believe the strain circulating in the state is much more infectious than previous variants, capable of transmitting between strangers with very minimal contact.
Those concerns prompted the Victorian government to extend the lockdown for Greater Melbourne for at least another seven days.
Australian Associated Press