While NSW has reported no recent cases of locally transmitted COVID-19 through to 8pm - the twelfth consecutive day of zero transmission - there have been three reports of new cases overnight.

Two cases have been reported in South Western Sydney and one in Western Sydney. These cases are under urgent investigation and will be reported in Thursday's daily count.

Three cases in overseas travellers in hotel quarantine were diagnosed in the 24 hours to 8pm last night, bringing the total number of cases in NSW to 4060.

There were 5970 tests reported in the 24-hour reporting period, compared with 5,385 in the previous 24 hours.

"Testing numbers have dropped recently, which is a concern," a statement from NSW Health said.

"NSW Health is appealing to the community to come forward for testing right away if you have even the mildest of symptoms like a runny nose or scratchy throat, cough, fever or other symptoms that could be COVID-19.

"This is particularly important due to the new cases reported overnight.

Testing is also important for people in the Hawkesbury and South Western Sydney areas, following yesterday's report that traces of virus were recently detected at two treatment plants: North Richmond in the Hawkesbury and West Camden in South Western Sydney."

NSW Health is treating 54 COVID-19 cases, including three in intensive care, none of whom are being ventilated.