MELBOURNE (AFP) - Australia confirmed two new swine flu cases on Sunday, taking its total number of infections to 16, as Health Minister Nicola Roxon highlighted concerns over how easily the virus was spreading.

Authorities in Victoria state said a 27-year-old man and 15-year-old boy in Melbourne tested positive for the virus and the boy's school would be closed for a week as a precaution.

Victorian Health Minister Daniel Andrews said the man appeared to have caught the flu from his 17-year-old cousin, who was diagnosed with it last week, while the boy apparently contracted it from a 12-year-old schoolmate.

The latest infections come after Australia on Friday raised its alert level following confirmation of the country's first case of human-to-human transmission of the A(H1N1) virus.

Roxon said she was concerned authorities could not explain how some of the infections had occurred and that the virus appeared to be extremely contagious.

"I think it's serious.... We do have a slightly worrying development that we have several cases where we cannot identify where they might have got the disease from, so they're not travellers, they're not immediate contacts of confirmed cases," she said.

Australia's declaration of a "containment" phase allows for the closure of schools and other public places and for the cancellation of major events, with a number of schools already shut. (AFP)