Australia's third largest city to enter three-day coronavirus lockdown

Australia's third-largest city will enter a three-day lockdown beginning late on Friday, as authorities seek to prevent the spread of a more contagious variant of Covid-19 first detected in Britain.

Brisbane's 2 million residents will be barred from leaving their homes for anything but essential business after a worker at a quarantined hotel in the city tested positive for the new strain of the virus.

"If we do not do this now, it could end up being a 30-day lockdown," state Premier Annastacia Palaszczuk said as she announced the lockdown to begin at 6 p.m. local time.

People must wear masks when they leave home for essential business, Palaszczuk said. Funerals and weddings can proceed, but with limits of 20 and 10 people respectively. Entertainment venues will close and restaurants and cafes will be allowed to provide takeaway only.

Authorities have not detected any new cases since Thursday when they reported the case of the worker at a hotel used to quarantine people who have recently arrived from overseas, but said they could not afford to delay action.

"We can't put it back in the box. We've got to act before we get the cases," Queensland Chief Health Officer Jeannette Young said.

Officials have identified and isolated 79 people who are close contacts of the female worker.

Prime Minister Scott Morrison tweeted the lockdown "will buy much needed time", as the case sharpens the focus on Australia's procedures on returning citizens and residents from overseas.

Morrison has convened a special meeting of state and territory leaders on Friday to consider tightening rules for international arrivals.

Australia has since March shut its borders to all non-citizens and permanent residents. It has also capped the number of people allowed to enter the country each week, and returnees must enter mandatory hotel quarantine at their own expense.

While the system has been widely credited with preventing major outbreaks, the majority of Australia's more than 28,500 cases can be traced back to quarantine hotels.