Authorities have imposed a snap three-day lockdown in south-eastern parts of Queensland, including Australia’s third largest city Brisbane, which began at 16:00 (06:00 GMT) on Saturday.
Fewer than 15% of Australians are fully vaccinated against the virus.
Queensland officials reported six new Covid cases there, all linked to a high school student who tested positive on Thursday.
Dr Jeannette Young, chief health officer in Queensland, told reporters they were tracing any contacts of those who had tested positive and said she thought there could be “an enormous number of exposure sites” in Brisbane.
“If anyone has any symptoms at all, this is the time – you must come forward and get tested immediately,” she said.
The restrictions imposed are the strictest yet in Queensland. People are only allowed to leave home to buy essential goods or carry out essential work, to exercise or to go for medical treatment.
Sydney’s measures will stay in place until at least 28 August.
The state of New South Wales recorded a further death and 210 fresh infections on Saturday, after five weeks of lockdown. Last Saturday police arrested dozens of demonstrators who protested against the restrictions.
On Friday he announced that once 70% of the country was fully vaccinated, lockdowns would become more targeted.