Sydney's 5 million residents are currently in lockdown. (Photo: AFP/Saeed Khan) - 

The Australian city of Sydney on Saturday (Jul 17) ordered a shutdown of building sites, banned non-essential retail and threatened fines for employers who make staff come into the office as new COVID-19 cases kept rising three weeks into a citywide lockdown.

Authorities in New South Wales state, of which Sydney is the capital, also banned hundreds of thousands of people in the city's western suburbs – the worst affected area – from leaving their immediate neighbourhoods for work, as they recorded 111 new cases in the prior 24 hours, up from 97 the day before.

"I can't remember a time when our state has been challenged to such an extent," New South Wales Premier Gladys Berejiklian told a televised news conference.

The city of 5 million people, Australia's largest, has been under lockdown since Jun 26, with a planned end date of Jul 30, after an airport transit driver brought the virus into the community and sparked an outbreak of the highly infectious variant, according to the authorities.

More than 1,000 people in the city and surrounding districts have since tested positive. Of most concern to health leaders is the number of infectious people who were active in the community before they tested positive, with 29 reported on Saturday, in line with previous days.

"We are chasing our tail in terms of the cases," state Chief Health Officer Kerry Chant said at the news conference.

New South Wales Police Deputy Commissioner Gary Worboys said the "tempo of the police response will increase" across Greater Sydney and regional areas.

People who lived in three of Sydney's local government districts - with a total population of 612,000 - were banned from leaving their district for work unless they were emergency workers. The city already has a work-from-home directive for businesses, but employers who told staff to attend the office could be fined A$10,000 (US$7,402).

Neighbouring Victoria state also reported a jump in daily COVID-19 cases to 19, from six the previous day, raising fears it may extend a short lockdown that was scheduled to end on Tuesday.

Victoria and Greater Sydney have a combined population of about 12 million people, meaning nearly half of Australia's population is under some form of lockdown.

All but one of the new cases in Victoria was active in the community before diagnosis, but every case was linked to a known chain of transmission, Victorian Health Minister Martin Foley said.

Australia avoided the high infection and fatality numbers of many other countries in the initial stages of the pandemic due to an assertive response that included closing borders, stay-home orders and economic stimulus measures.

But 18 months on, the federal government faces criticism over its sluggish vaccine roll-out. More than 10 per cent of Australia's 25 million people are fully vaccinated, according to government data, a fraction of the rates in the United States and Britain.

Even so, Australia's death rate from COVID-19, about 900 deaths out of about 31,500 cases, is still low by comparison.

The Australian economy had surged back to life after dipping into recession last year, but the latest lockdowns and state border closures threaten to tip it back into negative growth. No other states reported additional cases on Saturday//CNA