Premier Gladys Berejiklian and chief health officer Kerry Chant extended their condolences as they announced the deaths during the Wednesday morning update.

"Very sadly a male in his 20s passed away at home with COVID (in) south west Sydney overnight," Ms Berejiklian said.

"Obviously, our deepest condolences to his family and loved ones.

"It demonstrates again how this disease is lethal and affects people of all ages."

The man was a confirmed COVID-19 patient and was being cared for in his home while isolating, Dr Chant said.

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"He reached day 13, he was being followed up daily by nursing staff, and he had suddenly deteriorated," she said.

"I understand that death is also being referred to the coroner."

The man had not received any vaccinations against the virus, the premier and chief health officer confirmed, nor had the second person who died yesterday, a woman in her 80s who was diagnosed in July.

More than 105,000 tests were carried out on Tuesday, "a good, high number for us to be able to capture all the cases in the community," Ms Berejiklian said.

A total of 47 of the 233 cases to 8pm Tuesday were infectious while in the community.

Sewage monitoring has authorities extremely concerned there may be undetected cases in the Newcastle area.

"Concerningly there were very high rates detected in the sewage in the Hunter Valley and Newcastle area," Ms Berejiklian said.

"The sewage (has) detected high viral load, which suggests there could be undetected cases."

People are also urged not to mingle in apartment buildings, particularly in entries, don't share lifts or use facilities that may have been used by others.

In the Riverina, almost one in five people are fully vaccinated against COVID-19, new data has revealed.

Wagga's Dr Ayman Shenouda said it is a "pretty good number", considering the fact that it is a regional area.

This places the region at 13 out of the 28 geographic areas in the state. The Riverina falls just behind the Central Coast at 19.6 per cent fully vaccinated, and just ahead of the Capital Region at 17.9 per cent.

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