The three cases acquired COVID-19 in Sydney and were diagnosed while isolating in special health quarantine on the Mid North Coast.

MNCLHD chief executive Stewart Dowrick said these cases are close household contacts of a known positive case and are not locally-acquired cases.

The positive cases have not been moving about in the Port Macquarie-Hastings or Macleay communities while positive.

A 22-year-old woman and her three children from Sydney, plus passengers and crew, are in the health quarantine facility after police stopped a train at Kempsey on September 9.

Mid North Coast Police District officers received reports that the woman had failed to isolate after a positive COVID-19 test, and was travelling from Strathfield to Coffs Harbour with her three children.

Police said officers stopped the train at Kempsey about 10.40pm to remove the woman and her children from the train, before they were taken by NSW Ambulance paramedics to a special health hotel at Port Macquarie.

The woman and her children, as well as all other close contacts on the train, will remain in isolation at the health facility for the next 14 days.

NSW Health staff are now providing support to a total of 21 people who are in isolation at the health accommodation.

There has also been one new confirmed case at Booral near Stroud in the MidCoast local government area. This case is linked to a known case in the area and was infectious while in the community.

The MidCoast LGA, which includes the Manning, Great Lakes and Gloucester regions, south to Hawks Nest and Tea Gardens and inland to Stroud and Barrington Tops, falls in the Hunter-New England Health District.

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NSW Health's ongoing sewage surveillance program has detected fragments of the virus that causes COVID-19 at the Dunbogan treatment plant from samples taken on 8 September.

The Dunbogan sewage treatment plant serves around 8,500 residents of Dunbogan, Laurieton, Lakewood, West Haven, Camden Head and North Haven.

There was also a positive sewage detection at the Port Macquarie wastewater facility. The sample was taken on September 8.

The Port Macquarie sewage treatment plant serves around 54,000 residents of Port Macquarie, Sovereign Hills, Thrumster, Sancrox, North Shore and Settlement Point.

On September 5, the highway service centre at Kempsey became a 'venue of concern' after a confirmed case of COVID-19 transited through the region.

Testing sewage can help provide early warning of undetected infections in an area. Detection of virus fragments in sewage can also be due to shedding of the virus by someone who may have previously had the illness and may no longer be infectious.

It can also be the result of a person with COVID-19 who may have visited the community and has since left the area.

We are urging everyone to monitor for the onset of symptoms, and if they appear, to immediately be tested and isolate until a negative result is received.

If you are directed to get tested for COVID 19 or self-isolate at any time, you must follow the rules whether or not the venue or exposure setting is listed on the NSW Health website.

A full list of COVID-19 testing clinic locations and opening hours are listed on the NSW Government website at www.nsw.gov.au/covid-19/health-and-wellbeing/clinics

A total of 1262 cases of COVID-19 were recorded in NSW, health officials said on Sunday.

The new cases cover the 24 hours to 8pm on Saturday, with seven people dying from the virus in this time.

This included a man in his 20s from western Sydney, a woman in her 40s and a woman in her 50s from south-western Sydney and a man in his 50s from western Sydney.

Across NSW, 78.1 per cent of the over-16 population has received one COVID-19 vaccine, with 45.6 per cent now fully vaccinated.

From Monday, people across NSW who have received both doses of a COVID-19 vaccine will be allowed more freedoms.

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"For those who live outside the LGAs of concern, up to five fully vaccinated adults can engage in outdoor recreation in a person's LGA or within 5km of home. Children under 12 will not be counted in this total," NSW Health said.

NSW Health's ongoing sewage surveillance program has detected fragments of the virus that causes COVID-19 at Tamworth, Karuah, Dungog and Dunbogan treatment plants.

NSW Premier Gladys Berejiklian said people could look forward to freedoms at the 70 per cent double-dose vaccination rate, but "we can't afford to let our guard down".

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"There has been some stablisation in local government areas of concern," Ms Berejiklian said.

"However, the most concerning areas where the virus is picking up pace at the moment are in a couple of suburbs in south-western Sydney, as well as some suburbs in the inner Sydney and inner western areas."