Newcastle and Hunter residents have been urged to come forward for testing after "very high viral load" was detected in the region's sewage.
"There were very high rates of virus detected in the sewerage in the Hunter area," Ms Berejiklian said.
"The very high viral load suggests there could be undetected cases up around the Hunter area."
And it's not the only area on the NSW Health radar thanks to sewage detection testing.
Low levels of COVID-19 have been detected in Mudgee's Sewage Treatment Plant in the NSW central west and also on the NSW Mid-North Coast.
Virus fragments also have been found in sewage samples taken from the Coffs Harbour and Bonny Hills sewage treatment plants.
NSW recorded 233 new locally acquired cases in the 24 hours to 8pm on Tuesday. 103 are linked to a known case or cluster, 79 are household contacts and 24 are close contacts.
Chief health officer Dr Kerry Chant said health authorities were "very concerned" by the Hunter testing results.
She said the detection was from both the Shortland and Burwood waste water plants, as well as a "lower detection" at Belmont.
Dr Chant named Birmingham Gardens, Shortland, Maryland, Fletcher, Minmi, Cameron Park, Stockton and Fern Bay among the suburbs flagged as priorities for testing for anyone with even the mildest symptoms as efforts continue to work out where the shedding has come from.
Hunter New England Health public health physician Dr David Durrheim said the plants served about 400,000 people in the region.
The test results were on samples taken Monday and came back late on Tuesday night, Dr Durrheim said.
"This means there is someone in the community, or more than one person in the community, that are infected with COVID-19 or have visited our region infected with COVID-19 and they have shed viral fragments in their faeces," he said.
"Now is the time to hunt the virus down. We have to flush it out."
The full list of suburbs
- BURWOOD:Newcastle City area and surrounding suburbs of Dudley, Charlestown, Jesmond, Lambton, New Lambton, Mayfield, Elermore Vale, Wallsend, Kotara, Garden Suburb, Adamstown Heights, Kahibah, Highfields, Merewether, Waratah West, Georgetown and Carrington.
- BELMONT:Belmont, Warners Bay, Gateshead, Tingira Heights, Bennetts Green, Jewells, Redhead, Eleebana, Croudace Bay, Valentine, Marks Point, Blacksmiths, Pelican, Swansea, Swansea Heads, and Caves Beach.
- SHORTLAND:Shortland, Cameron Park, Minmi, Fletcher, Maryland, Birmingham Gardens, Wallsend, Callaghan, Sandgate, Stockton, Fern Bay and Mayfield West
The detection is the latest in a run of scares for the Hunter that the virulent Delta variant would spread out of Sydney and the Central Coast's lockdown.