A cluster of 65 cases is causing concern.
Residents in Sydney have been ordered to stay home as four local government areas in the city have been put into lockdown for at least a week.
Authorities have locked down several central areas of Australia's largest city to contain an outbreak of the highly contagious Delta variant of Covid-19.
Officials reported 17 new cases on Friday, taking the cluster to 65 cases.
Residents who live or work in Woollahra, Waverley, Randwick and the City of Sydney have been issued stay-at-home orders from 11.59pm on Friday.
“If you live or work in those four local government areas you should not leave your home unless you have to. What this does is make sure that we haven’t missed any chains of community transmission,” NSW Premier Gladys Berejiklian said on Friday morning.
She added: “This is in order for us to ensure this doesn’t take hold for weeks and weeks, and we believe this is a proportionate response to the risk.”
Residents of affected areas can leave home only if work or education is impossible at home, for exercise outside and to provide care for a relative.
Public health experts have been stunned by instances of people passing on the virus during brief encounters in shops and then quickly infecting close family contacts.
Due to the contagiousness of the strain, Berejiklian said the state is “likely to see more cases in coming days, mainly from household contacts”.
