Nine overseas travellers in NSW hotel quarantine have been diagnosed with COVID-19 as authorities detect more virus traces in sewage.
There are 72 active coronavirus cases across the state with health officials warning the public to remain vigilant.
"With the weather becoming warmer and people starting to attend more social gatherings, NSW Health is calling on the community to maintain the COVID-safe behaviours," a spokesman said on Sunday.
"Although there have been no locally acquired cases in NSW in recent days, now is not the time to drop our guard."
Members of the public are reminded to keep practising physical distancing and good hand hygiene, and get tested and isolate if they feel unwell.
No locally acquired cases were diagnosed in NSW in the 24 hours to 8pm Saturday.
Authorities are urging testing for symptomatic people in parts of west and northwest Sydney after traces of coronavirus were found in sewerage systems.
"The catchment takes sewage from approximately 180,000 people," NSW Health said of one network.
The traces were found in samples taken on Thursday from a waste water network which services parts of suburbs including Leppington, Catherine Field, West Hoxton, Hoxton Park, Edmondson Park, Prestons and Miller.
Traces were also found in a separate sewerage system, servicing 120,000 people in an area covering Quakers Hill, Bella Vista, Kellyville and Baulkham Hills.
"While detection of the virus in sewage samples could reflect the presence of older cases of COVID-19 diagnosed in these areas, NSW Health is concerned there could be other active cases," a statement read.
Authorities had previously urged people in Rouse Hill, Bowral and Moss Vale areas to get tested after virus traces were found in sewage.
Meanwhile hundreds of travellers from New Zealand are being contacted after a positive coronavirus case was confirmed in Auckland.
Those who arrived in NSW from NZ since November 5 have been sent a message with advice and are being contacted about a number of venues of concern in Auckland.
NSW Health said previously no passengers arriving in Sydney from NZ had reported having visited the locations and none had symptoms.
"Airlines will ascertain if passengers have attended these venues before they leave NZ and if they have, they will be not allowed to travel," the health department said.
All arrivals from NZ will be asked to monitor for even the mildest of symptoms and get tested and isolate if they appear unwell, NSW Health added.
NSW will reopen its border with Victoria on November 23. The southern state has recorded more than two weeks of consecutive zero-transmission days.
No quarantine will be required upon arrival or departure from the state.
NSW has recorded 4306 cases of coronavirus since the start of the pandemic.
