Sydney's COVID-19 cases rise, four Australian cities in lockdown

Around one in two Australians are under stay-at-home orders with Sydney, the country's largest city, under a two-week lockdown until July 9, while Perth, Brisbane and Darwin are in snap lockdowns until later this week.

Tough restrictions, including mandatory masks and curbs on gatherings, have been enforced in most other major cities.

The daily NSW new cases number was up slightly from the previous two days, but still below the peak of the current outbreak of 30 new cases reported on Sunday, and all 22 were linked to prior cases.

"New South Wales is demonstrating a steady rate of cases at this stage ... but to date our fears about huge escalation haven't materialised and we certainly want to keep it that way," state Premier Gladys Berejiklian told reporters in Sydney.

The state has recorded a total of around 170 new locally transmitted cases since the first infection was detected two weeks ago in a limousine driver who transported overseas airline crew.

Queensland reported three new locally acquired COVID-19 cases on Wednesday, the first day of a snap four-day lockdown imposed in state capital Brisbane after a person infected with the Delta variant visited several venues over 10 days while unknowingly infectious.

Perth, the Western Australia capital, is under a four-day lockdown until Saturday, while residents in the northern city of Darwin must stay home except for urgent reasons until Friday afternoon.

Lockdowns, tough social distancing, swift contact tracing and a high community compliance have helped Australia quash prior outbreaks and keep its COVID-19 numbers relatively low.