More than two million people in Brisbane were ordered into a three-day lockdown Monday after a cluster of coronavirus cases was detected in Australia's third-biggest city.

It is the second snap lockdown of Brisbane and the city's surrounds this year, coming after seven people tested positive for Covid-19 -- the first significant community outbreak in Australia in weeks.

"This is the UK strain. It is highly infectious. Now we need to do this now to avoid a longer lockdown," Queensland state Premier Annastacia Palaszczuk said.

"We've seen what's happened in other countries. I don't want to see that happen to Queensland, I don't want to see that happen to Australia."

Schools, restaurants and bars will close from 5:00pm Monday but people will still be allowed to leave home for essential work, to buy food, exercise and for medical care.

Wearing masks in public is also becoming mandatory across Queensland, after one infectious person travelled to the regional town of Gladstone.

The number of international flight arrivals will be halved, to ease pressure on hospitals also dealing with a surge in Covid-19 cases from neighbouring Papua New Guinea.

Australia has been relatively successful in curbing the spread of Covid-19, with just over 29,000 cases and 909 deaths during the pandemic to date.

However the country's vaccine rollout has been sluggish, with just over 500,000 shots administered so far in a country of 25 million.

Palaszczuk said lockdowns would "be part of the Australian way of life until everyone is vaccinated".

Before the announcement, Brisbane was among several Australian cities enjoying relaxed restrictions with residents able to freely attend events including concerts and sporting matches.