Hunter New England Health says three towns in the region have state-high levels of coronavirus in their sewage.
Public health controller Dr David Durrheim said on Sunday that he was concerned about Raymond Terrace, Williamtown and Medowie, where the level of viral detection in sewage was "as high as anywhere we've seen in NSW".
He urged anyone with "even the mildest of symptoms" to get tested and isolate immediately.
Dr Durrheim was also worried that three of the Hunter's five unlinked COVID-19 cases were in the Maitland area
He said the town had "high-risk transmission sites" at the Guzman y Gomez restaurant at Green Hills shopping centre, Maitland Christian School and Sudania cafe in High Street.
The Guzman y Gomez store is listed as an exposure site from 2.30pm to 8.30pm on August 7, 8 and 9 and from 5pm to 8.30pm on August 11.
The Hunter reported nine new cases on Sunday, a result NSW Premier Gladys Berejiklian described as "positive" and a "stabilisation".
Chief health officer Dr Kerry Chant said at the state's daily COVID update on Sunday that the "settling" of case numbers in the Hunter was pleasing.
Three of the new Hunter cases are in Newcastle, three in Port Stephens, two in Maitland and one in Lake Macquarie.
Eight of the cases are linked to known sources of infection and the other is under investigation.
The Hunter New England Health district has recorded 104 COVID-19 cases since August 5.
NSW recorded 415 new cases in the 24 hours to 8pm on Saturday.
The Hunter registered 24 cases on August 12 then five, 13 and nine on the following three days.
Dr Chant said health authorities were still concerned about the Maitland area and urged Hunter residents to remain vigilant about published exposure sites.
Another four people have died of COVID-19 in NSW, including an unvaccinated woman in her 50s in western Sydney, a woman in her 70s in Royal North Shore Hospital who had only recently had her first dose of a vaccine, an unvaccinated man in his 80s at Liverpool Hospital, and a woman at Royal Prince Alfred who had been vaccinated but had underlying chronic conditions.
Deputy Police Commissioner Michael Willing said police had issued eight infringement notices to people who "thought they could gather at a residence in Jesmond".
Police issued 31 infringement notices after breaking up a gathering of young people on the cliffs at Clovelly, in Sydney.
Dr Chant said the state's case numbers were "too high" and the community should stay at home for the next two weeks to bring them down.
"I am gravely concerned that the numbers will continue to escalate," she said.
Prime Minister Scott Morrison announced on Sunday morning that Australia had bought a million Pfizer does from Poland.
The first 530,000 doses, which are due to start arriving on Monday, will help vaccinate 20- to 39-year-olds in western Sydney.
Ms Berejiklian said NSW had reached 5 million administered vaccine doses and urged people to keep coming forward for jabs.
"Don't be too fussed about the type of vaccine you are offered," she said.