Australia's most populous state, New South Wales, reported a double digit rise in new cases of COVID-19 on Thursday.
Officials are fighting to contain an outbreak of the highly contagious Delta variant.
Eleven new cases were reported, taking the total in the latest outbreak up to more than 40.
State Premier Gladys Berejiklian warned that the state's capital, Sydney, was on edge:
"Since the pandemic has started, this is perhaps the scariest period that New South Wales(NSW) is going through. . . . It is a very contagious variant but at the same time we are at this stage comfortable that the settings that are in place are the appropriate settings, but that's so long as everybody does the right thing."
And with that stern message came new restrictions, including mandatory mask wearing in all indoor locations in Sydney and home gatherings are limited to five people.
Restricted movement regulations have also been imposed for seven council districts in the east and inner west of the city.
Western Australia responded by closing its border to NSW.
And neighboring New Zealand is on alert and watching the situation closely. It reported no new local cases on Thursday, but there have been concerns after an Australian tourist tested positive upon returning to Sydney after a weekend visit.