Australia has reported 723 new Covid-19 cases in a day in Victoria state, its worst day ever as a surge in infections thwarts weeks of efforts to keep the virus at bay.

A total of 13 more people had died, bringing the state’s death toll to 105.

Infections had gradually decreased earlier this week, with 295 new cases recorded on Wednesday, July 29.

A six-week lockdown in the city of Melbourne was bringing the outbreak under control.

The decrease raised hopes the lockdown of the city of 5 million people was working.

Most of the newest cases are in metro areas while there has been a significant jump in regional communities, Victoria Premier Daniel Andrews told reporters.

Mask-wearing is compulsory across the state, extending the order from just Melbourne.

Fear of more damage with lockdown

The stay-at-home order in Melbourne began three weeks ago.

Its extension and widening across other parts of the state is feared to further damage the economy.

Health authorities also fear the virus is spreading to other states and territories, most of which have gone weeks without recording community transmissions.

Queensland state is ramping up testing despite having closed its border to Victoria and the Greater Sydney area.

This was after two women there who visited Melbourne didn't self-isolate on their return.

Instead, they went to schools, restaurants and shopping centres for eight days unchecked before returning a positive result.

The resurgence in Victoria is placing the health-care system under stress.

Victoria state has said it will suspend all but the most urgent elective surgeries in Melbourne as it seeks to free up hospital beds and nurses to fight a spike of cases in such facilities.

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