SYDNEY — Residents of four neighbourhoods of central Sydney were ordered to remain at home for a week on Friday (June 25) to contain a growing outbreak of the highly contagious Delta variant of Covid-19.

Several dozen cases have been reported this week, linked to a limousine driver infected when he transported an international flight crew from Sydney airport to a quarantine hotel.

The decision to lock down from midnight Friday came as the cluster grew to 65, with state premier Gladys Berejiklian ordering anyone who lived or worked in the affected areas over the past fortnight to stay at home.

Workers in the city's central business district were included in the restrictions over fears commuters were potentially spreading the virus into other parts of the city, Ms Berejiklian said.

"We've done better than expected in terms of contact tracing and getting on top of all those links," she said.

"But what this does is make sure that we haven't missed any chains of community transmission."

Those under the lockdown orders would only be allowed to leave home for essential reasons, including buying food or if they were unable to work from home.

An earlier ban on Sydneysiders leaving the city was also extended until next Friday as traces of the virus were detected in sewage in the far-flung outback town of Bourke, about nine hours drive northwest of Sydney.

Australia has been among the world's most successful countries in containing Covid-19, with just over 30,000 cases and 910 deaths.

But the virus has repeatedly escaped Australian hotels used to quarantine returning travellers, and health experts say the outbreaks will continue until large numbers of Australians are vaccinated. AFP