Australia's second most populous state Victoria entered a five-day lockdown on Saturday as authorities raced to prevent a third wave of Covid-19 cases sparked by the highly infections UK variant.

One new locally acquired case was confirmed in the past 24 hours, Victoria health authorities said on Saturday, taking the number of active cases in the state to 20.

‘A lot of people will be hurting today. This is not the position Victorians wanted to be in but I can't have a situation where in two weeks' time, we look back and wish we had taken these decisions now,’ Victoria Premier Daniel Andrews told reporters on Saturday.

Andrews said Prime Minister Scott Morrison had agreed to stop all international flights to Melbourne through Wednesday, after five en-route, with about 100 passengers, land on Saturday.

The cluster that triggered the renewed restrictions stemmed from a quarantine hotel at Melbourne airport.

Streets in downtown Melbourne, the state's capital, and its suburbs were almost empty early Saturday, with people ordered to stay home for all but essential shopping, two hours of outdoor exercise, caregiving, or work that cannot be done from home.

Among the ‘essential’ work, play at the Australian Open, the year's first Grand Slam tennis event which runs to Feb. 21, continued, but fans were banned through Wednesday. Thousands were forced to leave mid-matches before midnight on Friday.

The lockdown, which has shut restaurants and cafes for all but takeaway, hit just as Melbourne had geared up for the biggest weekend in nearly a year, with Lunar New Year celebrations, Valentine's Day and Australian Open crowds.

Melbourne last year endured a 111-day lockdown, one of the strictest and longest in the world at the time, to stem a coronavirus outbreak which lead to more than 800 deaths.

‘It's the busiest weekend of the year for us. I'm sitting here making 178 heartbreaking phone calls to see if I can get them to rebook,’ said Will Baa, owner of Lover, a restaurant in the hip district of Windsor.

‘It is quite soul destroying. But we're resilient. Just fingers crossed that it only does extend for the short period of five days,’ he said.

More broadly, Australia is rated among the world's most successful countries in tackling the pandemic, largely because of decisive lockdowns and borders sealed to all but a trickle of travellers. With a population of 25 million, there have been around 22,200 community cases and 909 deaths.

New Zealand on Saturday reported one death of a patient with Covid-19. The person had been taken to hospital from quarantine for an unrelated condition and later tested positive. That case has yet to be included in the country's total of 25 Covid-19 deaths.