Authorities said there is still no evidence that the virus has reached Australia's poultry farms, many of which have been under strict biosecurity measures since H5N1 was first detected in the country in June.

Agriculture Minister Julie Collins said testing confirmed H5N1 bird flu in a group of 49 dead and 35 sick terns found by helicopter surveillance on rocks off Cape Jaffa, 250 km (155 miles) from Adelaide on Friday.

Officials Warn of Wider Wildlife Spread

'Australians should expect to see more spread and larger numbers now of wildlife being affected,' she told reporters in Canberra, the capital.

'This is the first confirmed case of a mass mortality,' she added. 'Once the H5 bird flu is spreading in wildlife and the natural environment, it is not possible to avoid significant losses, which is what we're starting to see now.'

Australia's tally of 74 confirmed cases is spread as wide as the states of Western Australia and Queensland, though most cases were in South Australia, Collins said.

Biosecurity Measures Intensified

Australia and New Zealand - which saw its first H5N1 case last month - have spent years bracing for the virus, with steps such as tighter biosecurity at farms, testing of shore birds, vaccinating vulnerable species and war-gaming response plans.

The virus has killed hundreds of millions of birds and mammals in recent years, causing billions of dollars in losses to poultry farmers, infecting cattle in the United States and littering beaches with corpses of birds and seals.

H5N1 bird flu can infect humans who have contact with infected animals. But the number of cases worldwide is small and officials say the risk to humans is low.

(With inputs from Reuters)