Melbourne: Health authorities are using what they describe as the world’s first saliva test for coronavirus, in Australia's second-largest city where the disease is spreading at an alarming rate.

Officials say 49 people tested positive for COVID-19 in Melbourne on Sunday and only four cases were detected elsewhere in Australia.

Australian Deputy Chief Medical Officer Nick Coatsworth told Australian Broadcasting Corp. on Monday, that the saliva test was being rolled out in Victoria state, where Melbourne is the capital, and its effectiveness was still being tested.

Coatsworth said the less-comfortable nasal test remained the preferred option and may be more accurate, but the saliva test will be great, particularly for kids.

Victorian Chief Health Officer Brett Sutton said authorities were close to losing control of the spread while pandemic restrictions were easing elsewhere in Australia.

l think it's a genuine challenge now. I think we're right at the edge in terms of being able to manage it, Sutton said.

We know that as three-quarters of the country goes back to a normal way of living, it becomes even more challenging to tell people that it's not the same here and that they've got to go on with a more constrained life, Sutton added.

Melbourne and Sydney, Australia's largest city, began with the largest numbers of cases because of the large numbers of international travellers they receive, Sutton said.

Melbourne's colder weather during the current Southern Hemisphere winter might also play a part in the city's great community transmission, he said.