MELBOURNE (REUTERS) - Australia's New South Wales (NSW) state recorded three new coronavirus cases on Sunday (Jan 10) as a three-week lockdown for about quarter million of people in Sydney's northern beaches suburbs eased.

NSW Premier Gladys Berejiklian said masks in public places and on transport will remain mandatory for greater Sydney and some public gathering restrictions will continue as the recent outbreak of the pandemic there still poses risks.

"It only takes one or two cases to get out of control or undetected line of transmission to get out of control for all of us to be in a situation where we have to consider making things tighter," Ms Berejiklian said at a televised press conference.

NSW and Sydney, Australia's largest city, have been isolated from the rest of Australia by state border closures or 14-day mandatory quarantine rules for interstate arrivals from NSW, following a mid-December outbreak.

There were no new cases reported on Sunday in either Victoria or Queensland, both of which share borders with NSW.

Brisbane, the capital of Queensland, was midway through its three-day strict lockdown on Sunday after the discovery of a single case of the Britain-linked virulent new coronavirus variant.

Brisbane's case, the first time the highly transmissible variant linked to Britain was recorded in a community in Australia, and several other cases of the new variants recorded in managed hotel quarantine, have put the country on high alert.

Thanks to strict and swift measures, high rates of community compliance and aggressive testing and tracing, Australia has been more successful than most advanced economies in managing the pandemic, with total infections at around 28,600 and 909 deaths so far.