Australia's Covid-19 response team holds urgent meeting amid outbreak

Australia's Covid-19 response committee is due to hold an emergency meeting on Monday as outbreaks of the highly contagious Delta variant across the country prompted a lockdown in Sydney and renewed restrictions elsewhere.

Around 18 million Australians, or around 70% of the population, are now under some form of lockdown or Covid-related restrictions as officials grapple with Covid-19 flare-ups in almost every state or territory.

"I think we are entering a new phase of this pandemic, with the more contagious Delta strain," federal Treasurer Josh Frydenberg told the Australian Broadcasting Corp on Monday, adding Australia was facing a "critical time" in its fight against Covid-19.

The national security committee, chaired by Prime Minister Scott Morrison, will be briefed by the country's chief medical officer later on Monday, Frydenberg said.

Sydney, Australia's most populous city and home to a fifth of Australia's 25 million people, was plunged into a two-week lockdown over the weekend.

Eighteen new local cases were reported in New South Wales state on Monday, compared with 30 a day earlier, taking the total infections in the latest outbreak to 130 since the first case was detected nearly two weeks ago in a limousine driver who transported an overseas airline crew.

"We have to be prepared for the numbers to bounce around and we have to be prepared for the numbers to go up considerably," Premier Gladys Berejiklian told reporters in the state capital Sydney.

"With this strain, we are seeing almost 100% transmission within households."

The northern city of Darwin entered a two-day lockdown on Sunday, prompted by the detection of the Delta variant of the virus - unrelated to the Sydney outbreak - in a fly-in, fly-out (FIFO) gold mine worker after he had left the facility.

Queensland state on Monday reintroduced mandatory masks and limited home gatherings in several areas, including state capital Brisbane, following a similar move by Western Australia officials for state capital Perth. Restrictions remain in place in Victoria state capital Melbourne and national capital Canberra.

A health alert was issued over the weekend for hundreds of passengers after an infected Virgin Australia cabin crew member worked on five different flights covering Brisbane, Melbourne and Gold Coast.

Australia has so far fared much better than many other developed countries in tackling the spread of the coronavirus, with just over 30,450 cases and 910 deaths.

Lockdowns, tough social distancing rules and swift contact tracing have helped the country successfully suppress prior outbreaks but the fast moving Delta variant has alarmed health authorities.