Australia's second-largest city Melbourne has entered the country's toughest lockdown yet, sparking a fresh wave of anxiety and confusion over ever-tougher regulations, AFP reported.

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.