Sydney sees worst day of 2021 as Delta COVID-19 outbreak spreads

New South Wales (NSW) reported 38 new local cases, up from 27 a day earlier, as its capital Sydney prepares for a third week of a lockdown.

"We don't want to prolong the lockdown, we don't want to see Sydney or New South Wales going in and out of lockdown until we have the vast majority of our population vaccinated," NSW Premier Gladys Berejiklian told reporters in Sydney.

Berejiklian implored residents to limit visits to family as data suggested the virus was spreading during such meetings, and urged people with flu-symptoms to take their entire family for COVID-19 tests due to the highly transmissible Delta strain.

She has promised this would be the last lockdown Sydney would need to endure in the pandemic although only around 10% of the country has been fully vaccinated.

Of Thursday's cases, 26 were either in isolation throughout or for part of their infectious period, while 11 spent time in the community while they were infectious. One case is under investigation.

Total infections neared 400 amid the largest outbreak of 2021 in the state, since the first case was detected in the city more than three weeks ago in a limousine driver who transported overseas airline crew.

A strict stay-at-home order had been enforced in Sydney, Australia's largest city and home to a fifth of the country's 25 million population, since June 26 for two weeks restricting people's movements and limiting gatherings.

That was extended on Wednesday until July 16 after restrictions failed to curtail the spread with officials frustrated after finding new infections linked to illegal gatherings and people flouting social distancing rules.

Australia has fared much better than many other developed countries in keeping COVID-19 numbers low, with just under 30,900 cases and 910 deaths, however, a slow vaccination rollout has taken the shine off some of this success.