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."
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.
Hunter residents and the region's MPs have expressed outrage since a flurry of text messages informed roughly 5500 people their booked appointments to receive Pfizer vaccines would not go ahead.
Health authorities advised their doses were among those seconded to Sydney to vaccinate Year 12 students in hot spots so they could complete their exams.
Asked about Lake Macquarie residents' concerns at having their appointments cancelled just days before the detection, NSW Health Minister Brad Hazzard said "what we really need from them is that they go and get tested if they have symptoms".
"Dr Chant and the entire public health team need to have the data," Mr Hazzard said.
"As for Pfizer, I think we've talked about that until the cows come home so we won't go into that again."
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Dr Chant also urged everyone with symptoms to go home immediately after a test, and said testing could help authorities determine what was behind the result.
Ms Berejiklian said she anticipated case numbers to get worse but said without the lockdown the state's daily figures would "inevitably in their thousands".
"I actually think they will get worse," Ms Berejiklian said.
"If you look at the number of people infectious in the community it suggests we haven't reached their peak.
"the fact we're only at a couple of hundred a day, which is serious in itself, demonstrates how much work we've taken to keep the virus at bay. The challenge for us is we need to do more than keep the virus at bay."
A man in his 20s died at his home in Sydney on Tuesday evening, which Ms Berejiklian said "demonstrates again how this disease is lethal and affects people of all ages".
The man had not received any dose of any vaccine.
"As we understand it the death happened quite suddenly," Ms Berejiklian said.
"People who are vaccinated are staying out of hospital, are staying out of ICU."
More than 105,000 people were tested in the 24-hour period.
Federal data shows that vaccination rates in parts of the Hunter are languishing, with just one in seven people over the age of 15 vaccinated in the region excluding Newcastle.
The Belmont vaccination hub is also expected to start offering AstraZeneca appointments from Wednesday, Hunter New England Health has advised.
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