Melbourne lockdown australia
© William West/Agence France-PresseAustralia's second city Melbourne has entered the country's toughest lockdown to date
Australia's second-largest city entered the country's toughest lockdown yet on Thursday, sparking a fresh wave of anxiety and confusion over ever-tougher regulations.

Melbourne's streets were visibly quieter as non-essential businesses were forced to shutter under new coronavirus rules expected to be in place for six weeks. A second lockdown for the state capital of Victoria began in early July but additional regulations came into force overnight, requiring hundreds of thousands more people to stay at home.

Residents are still allowed to go out during the daytime for exercise and food, or for work if their business is deemed essential.

Prime Minister Scott Morrison warned the latest lockdown would cost the Australian economy up to US$9 billion and push the unemployment rate back to 13 percent after a slight recovery.

He also said additional mental health support would be rolled out for Australians "working through the stress, and anxiety and strain" of lockdowns.

"Not being able to connect with friends and loved ones, concerns about employment, all of this takes a toll," Morrison said.

While the rest of Australia continues to see only a handful of new infections daily, Melbourne -- with its population of around five million -- is still recording hundreds per day. On Wednesday Australia saw its deadliest day of the pandemic to date, with 15 coronavirus deaths and a record 725 new cases in Victoria alone.

"While it's frustrating that Victoria's numbers have not trended downwards, it's also true the state has successfully avoided the kind of exponential increase in cases seen in many other countries," said Erin Smith, an emergency response expert at Edith Cowan University.

She added that daily statistics were yet to reflect the introduction of a curfew and other measures earlier this week.

Wave after wave of new rules and a myriad of exceptions to keep key parts of the economy open have left many confused about what they can do and when they can do it.

Lengthy daily television appearances by Victoria's state premier have featured detailed explanations about staffing at construction sites above three storeys being cut to 25 percent, or staffing limits for red-meat abattoirs versus poultry abattoirs.

While most residents appear to have heeded warnings and are keen for the lockdown to work, the measures have been opposed by some vocal critics. One group has announced a city centre protest for this Sunday, prompting Victoria police to warn that such a gathering would put "lives at risk".

"This selfish behaviour will absolutely not be tolerated," officers said, promising a "highly visible presence" around the city, hefty fines and arrests if necessary.

Australia has so far recorded almost 20,000 coronavirus cases and 255 deaths.