Young children, older Australians and other vulnerable people are being urged to get vaccinated for COVID-19 and influenza amid fears a range of viruses could create a perfect winter storm.

Forecasting ahead of the colder months is tricky but health officials are monitoring trends and considering a potential early start to the flu season, NSW Chief Health Officer Kerry Chant said on Tuesday.

Health insurer Bupa went a step further, warning of a "triple pandemic". It said northern hemisphere modelling indicated winter illnesses will arrive earlier than expected in Australia and be worse than last year, likely hospitalising more people.

"It's really very difficult to predict," Dr Chant told reporters on Tuesday.

"We are considering the potential early start to the flu season and a protracted flu season."

Influenza is expected to begin circulating with COVID and respiratory syncytial virus (RSV) over winter, Dr Chant said.

COVID transmissions and hospitalisations have also increased, particularly in recent weeks - a trend elderly people and other vulnerable groups particularly need to take note of.

About 1000 people in NSW are currently hospitalised with COVID, 20 of them in intensive care.

Influenza shots are free in Australia for children under five, Indigenous people, pregnant women, people with asthma and other serious health conditions and anyone over 65.

These groups are most at-risk from the flu, the Australian Medical Association says.

Shots are available at GP clinics and can also be accessed at pharmacies for adults and children over five.

Australia has already recorded more than 21,000 cases of flu this year - far more than during the pandemic.

Royal Australian College of General Practitioners president Nicole Higgins said people have been travelling more and stopped measures like wearing masks and washing hands, which has allowed flu to spread.

In the US, hospitalisation rates are significantly higher this season than last.

Those flu trends would likely be mirrored in Australia, Bupa's chief medical officer Tony MacDermott said.

"We're anticipating a perfect storm of flu, COVID-19 and other flu-like viruses to come together this winter," he said.

NSW Premier Chris Minns urged people to get vaccinated to protect themselves, their families and the health system.

Last flu season, about 40 per cent of people in the state had their flu shot. Authorities hope to reach 50 per cent this time.

"We all want to make sure our nurses, our paramedics, our doctors, those that work in the health system are not rushed off their feet during the busy winter period," Mr Minns said.

All adults are eligible for COVID boosters six months after their last infection or six months after their most recent shot.

Babies younger than six months are not eligible for a flu shot.