Health officials have sounded an alarm over a rise in rare COVID-mimicking bacterial infections that can cause disability and death.

Cases of invasive meningococcal disease and invasive group A streptococcus have been increasing over recent weeks, according to NSW Health.

Rates of IMD were above average across the state as 2022 drew to a close while iGAS cases have increased in Australia and overseas.

Health Protection NSW executive director Dr Richard Broome said it was important the community be aware that while these illnesses were rare, they were severe enough to possibly cause permanent disability or death.

These infections sometimes mimicked symptoms of COVID-19 or influenza in their early stages, and could occur at the same time as a viral infection, he said.

"Rapid intervention and effective treatment for invasive bacterial infections are available and can be lifesaving. We urge people to pay close attention to symptoms, trust their instincts, and seek urgent medical care if symptoms worsen or if they or the people they care for appear very unwell," he said.

"While notification data on iGAS has only recently become available in NSW, the number of people unwell with the condition has clearly increased here and across the world."

NSW had 137 cases of iGAS confirmed between September and December last year while 36 cases of IMD were reported across the state in 2022.

In general, symptoms of serious illness include fever, rapid heart rate, cold hands or feet, mottled skin, tiredness, confusion, nausea, vomiting or abdominal pain.

Young children who have been infected may be irritable, have difficulty waking up, refuse to eat, urinate less often and have difficulty breathing.

Symptoms of IMD include severe headaches, neck stiffness, discomfort in bright lights, or joint or limb pain.

A rash of red-purple spots or bruises often occurs later on in the illness.

iGAS can cause muscle aches or a red and painful fast-spreading skin infection consisting of pus or ulcerations.

Bleeding or vaginal discharge can also occur in women who are pregnant or who have just given birth.