Two cases in Hamilton were Newcastle's only cases on Thursday.

Dr David Durrheim said four days of 10 cases was "cause for celebration".

"We are a little concerned that the testing rates across the region have actually dropped," he said.

Dr Durrheim said fever and fatigue had been signs of Omicron infections to date.

"If you get even the mildest new respiratory systems ... it may be COVID," he said.

"Get a test."

A Macquarie Hills case initially listed in Hunter New England Health's update was later removed and replaced with a case identified in Taree, Midcoast's fourth alongside three from Harrington.

Of the new cases in Hunter New England seven were infectious in the community and eight were linked to existing cases or clusters.

There are 315 total active cases in the health district.

Armidale had two cases, while Moree Plains and Gunnedah both had a single case.

Fragments of the virus were also detected in sewage at Murrurundi, health officials said, where there are no known cases.

A sixth Omicron case has been confirmed in NSW. Health authorities said the international arrival was isolating in Sydney.

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