In Wednesday's daily update, NSW Health said that it's ongoing sewage surveillance program had detected fragments of the virus that causes COVID at the Yamba, Bathurst and Orange sewage treatment plants in recent days.

The Yamba sewage treatment plant serves about 6,500 people, the Bathurst sewage treatment plant serves about 36,600 people and the Orange sewage treatment plant serves around 40,000 people.

"These detections are of particular concern and everyone in these areas are urged to monitor for the onset of symptoms, and if they appear, to immediately be tested and isolate until a negative result is received," a statement from NSW Health said.

"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.

"It remains vital that anyone who has any symptoms or is a close or casual contact of a person with COVID-19, isolates and is tested immediately. When testing clinics are busy, please ensure you stay in line, identify yourself to staff and tell them that you have symptoms or are a contact of a case."

It comes as NSW recorded 633 new locally acquired cases of COVID in the 24 hours to 8pm Tuesday night.

Of these locally acquired cases, 158 are linked to a known case or cluster - 145 are household contacts and 13 are close contacts - and the source of infection for 475 cases is under investigation.

Of the 633 locally acquired cases reported to 8pm last night, 224 are from South Western Sydney Local Health District, 216 are from Western Sydney LHD, 54 are from Nepean Blue Mountains LHD, 52 are from Sydney LHD, 24 are from South Eastern Sydney LHD, 23 are from Western NSW LHD, 15 are from Hunter New England LHD, six are from Northern Sydney LHD, four are from Illawarra Shoalhaven LHD, four are from Far West LHD and 11 cases are yet to be assigned to an LHD.

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