A 45-year-old man has become the first person with swine flu to die in New South Wales and the 10th in Australia.

The man was not tested for swine flu until he died at Sydney's Nepean Hospital on Monday after collapsing at his home that day.

The director of the NSW Health Department's communicable diseases branch, Jeremy McAnulty, says the 45-year-old's underlying illness made him more susceptible to swine flu.

Dr McAnulty says the man had been sick with symptoms of the flu for several days.

"The coroner is investigating the exact circumstances of the death," he said.

"We understand the person died and had a complicated illness but after death, tests were taken and H1N1, or human swine influenza, was identified in the tests done.

"How much of that infection contributed to his death, we don't know at this stage and we'll be awaiting a report from the coroner."

The department says details of death could not be released until the man's family was notified of the test results and offered counselling.

Child dies

Yesterday, health authorities revealed a three-year-old Victorian boy was the first child in Australia to die with the virus.

The circumstances surrounding the death are unclear but federal Health Minister Nicola Roxon says it is not cause for alarm.

Ms Roxon says most children will not become seriously ill but parents should seek medical advice if they are concerned about their child's heath.

"I think we've seen clearly and been able to assure parents that for the vast majority of children, they will have very mild symptoms. They will recover," she said.

"I do want to assure people that they should not be unduly alarmed."

Seven Victorians and two Western Australians have died with swine flu.

A total of 4,568 people have tested positive for swine flu across Australia, 1,079 of them in New South Wales. Of those, 881 cases have been in Sydney.

Authorities say people with symptoms of the flu should seek medical help if their condition deteriorates.