Australia reported another spike in new coronavirus cases Monday, as a lockdown in the country's largest city Sydney failed to halt a rapidly growing cluster of cases.

Health authorities reported 112 cases in Sydney in the last 24 hours, a record for this wave of infections, despite a citywide lockdown that is in its third week.

The virus has now spread to neighbourhoods across the sprawling city of five million people.

New South Wales state premier Gladys Berejiklian said many of the latest infections were passed between family members and close friends who met despite a ban on meeting anyone outside your household.

Sydneysiders are currently ordered not to leave home unless for food shopping, medical treatment or daily exercise.

"If you put yourself at risk, you're putting your entire family -- and that means extended family, as well as your closest friends and associates -- at risk," Berejiklian warned.

Sydneysiders are currently ordered not to leave home unless for food shopping, medical treatment or daily exercise
Sydneysiders are currently ordered not to leave home unless for food shopping, medical treatment or daily exercise AFP / Saeed KHAN

On Saturday a woman in her 90s died hours after testing positive for Covid-19, the first death from a locally acquired infection in Australia this year.

Sydney's lockdown is slated to end Friday but authorities say that the target is now "highly unlikely" to be met.

The city is cut off almost entirely from the rest of the country under local travel bans.

New South Wales has recorded a total of 678 new infections since the latest outbreak began mid-June.

While that is low compared to most global cities, Australia has taken a zero-tolerance approach to community transmission throughout the pandemic.

Authorities have been quick to impose restrictions in an attempt to stamp out clusters early, and the country's borders remain largely shut. Only about 10 percent of Australians fully vaccinated.