With just a week until winter, less than half of the elderly population in NSW have had a flu vaccination, as cases of the potentially deadly infection surge.

Influenza infections have spiked over the past week, with more than 2100 cases recorded - up 66 per cent on the previous week, according to the NSW respiratory surveillance report published on Thursday.

Chief Health Officer Kerry Chant says 49 per cent of people aged 65 and older have had their flu vaccine this winter.

"We need to get that vaccination coverage much higher," Dr Chant told reporters.

Health experts expect high levels of flu across the winter months, after the season kicked off early.

"There are high levels of COVID-19 circulating in the community and with a rapid increase of influenza cases this week, it is also important people continue to take simple precautions to protect themselves and each other," Dr Chant said.

Health Minister Ryan Park said boosting vaccine coverage across the community was critical.

"Those in the 65-plus age group, we need to see that vulnerable group within our community start to accelerate in terms of our vaccination levels," he said.

Increases in flu cases last week were most notable in children between the ages of zero to four, and five to 16.

COVID-19 remains the most common virus in the community, although levels remained stable.