MELBOURNE (AFP) - Australia's second-biggest city will make it compulsory to wear a mask in public, the authorities announced on Sunday (July 19), as Melbourne steps up efforts to bring the coronavirus outbreak under control.

Victoria state, which includes Melbourne, now has nearly 3,000 active cases of Covid-19 after a further 363 infections were reported on Sunday despite a 10-day lockdown.

Victoria Premier Daniel Andrews said more than five million people in Melbourne and neighbouring Mitchell Shire would be required to wear a mask or other face covering in public spaces from midnight Wednesday (July 22) into Thursday.

"Most of us wouldn't leave home without our keys, we wouldn't leave our home without our mobile phone," he told a press conference.

"You won't be able to leave home without your mask and then wear it where it is absolutely essential to stop the spread of this virus."

Failure to comply with the new rule will mean an A$200 (S$194) fine - though Mr Andrews said "common sense" discretion would be applied to activities such as running or visiting a bank.

Bandanas and scarves will be acceptable as face coverings until the state can boost supplies of masks, Mr Andrews said, adding that anything was "better than no face covering at all".

The decision makes Melbourne the first place in the country to mandate the use of face coverings.

Mask-wearing is not common in Australia and has not been part of the country's Covid-19 response until now.

Australia's other states and territories have closed their borders to people from Victoria in a bid to stop the outbreak from spreading, as most regions have not reported any new locally transmitted infections for weeks.

But the contagion has reached Sydney, where locally transmitted cases have spiked in recent days after an initial cluster emerged from an infected Melbournian who visited a popular pub.

Australia has reported almost 12,000 cases of Covid-19 nationwide and 122 deaths in a population of about 25 million.