Lake Macquarie added nine fresh cases in Wednesday's update, the most of any part of the health district.

Four were in Cardiff, another four in Macquarie Hills and the ninth at Gateshead.

One case in Newcastle, in Wickham, was the only other Hunter infection as authorities found six Midcoast cases, five in Moree Plains and another in Armidale.

The Midcoast cases were in Wingham, Taree and Cundletown.

Public health physician Dr David Durrheim said it was crucial that precautions were taken in high-risk settings.

He urged doors and windows "thrown wide open", crowding prevented and activities shifted outdoors as much as possible.

"Across Hunter New England since schools have opened up we've seen a number of outbreaks, particularly in primary schools," he said. "We've seen over 70 primary schools affected by COVID in the schools, and 40 per cent of those we've seen transmission between children."

One element of those cases had been "quite intriguing", he said.

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"School teachers who double vaccinated and are wearing masks have not been impacted," Dr Durrheim said.

"Teachers are obviously being protected from COVID by being double vaccinated."

Dr Durrheim said a number of returning international travellers had tested positive over the past week after returning to the Hunter.

"This is an important to all of us that the northern hemisphere is seeing a surge in cases," he said.

"Anybody returning from overseas travel should really restrict their movements in the first week after their return."

Hunter New England Health said eight of the 22 cases that emerged in the 24 hours to 8pm on Tuesday were isolated while infectious, and 19 were linked to known exposures or clusters.

Despite the health district's improvement, its daily totals remain the highest in regional NSW.

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