SYDNEY - AUSTRALIAN authorities were attempting on Friday to trace the movements of two people confirmed to have contracted swine flu without having travelled overseas, as the number of cases here hit 11.

Four new cases of the virus were confirmed overnight and on Friday, including a 10-year-old girl who was a classmate of a Melbourne boy who fell ill, along with his two brothers, after returning from a US holiday last week.

A 25-year-old man who flew into Melbourne from Los Angeles Tuesday had also been diagnosed with swine flu, while a 17-year-old boy, also from the southern city, was confirmed to be carrying the virus.

A teenaged girl from Adelaide became South Australia state's first confirmed case, and authorities were trying to ascertain how she and the Melbourne teen had contracted the disease, said national Health Minister Nicola Roxon.

Neither had been overseas or had known contact with identified cases, and intensive tracing of their movements was now under way, she said.

Authorities have warned community transmission of the highly infectious influenza was 'inevitable', and Roxon said the confirmed cases could rise on an almost hourly basis.

Alan Hampson, a consultant to the World Health Organisation, said there was a high probability the virus would continue to spread, but Australia's pandemic plan did not yet need to move from the 'delay' to 'containment' phase.

Such a shift would allow for the closure of schools and other public places such as cinemas and nightclubs and cancellation of major sporting events.

More than 11,000 cases and 85 deaths have been recorded since the outbreak of A(H1N1) influenza emerged in Mexico and the United States a month ago, and the world remains at flu alert level five, signalling an 'imminent pandemic'. -- AFP