* PM Ardern extends Auckland lockdown by 4 days
* Level 2 restrictions for rest of country also extended
* Masks made mandatory on public transport
* Australia likely to post lowest single-day case rise in weeks (Updates Australian COVID-19 cases, adds quote)
By Colin Packham and Renju Jose
SYDNEY, Aug 24 (Reuters) - New Zealand Prime Minister Jacinda Ardern on Monday extended a coronavirus lockdown in the country's largest city until the end of the week and introduced mandatory mask wearing on public transport across the nation.
Ardern said the four-day extension in the city of Auckland was critical to enable the country to step down its scale of emergency restrictions - and remain at less restrictive levels.
"We want both confidence, and certainty for everyone," Ardern said during a televised media conference.
The Auckland lockdown, imposed on Aug. 11 after officials detected the country's first locally acquired cases of COVID-19 in more than three months, had been scheduled to end on Wednesday.
It will now end on Sunday night. The city's step down from Level 3 to Level 2 restrictions will be made gradually from Monday, Ardern said. 150 people have been diagnosed as part of the cluster that originated in Auckland, which is home to 1.7 million people, but daily new case numbers have slowed to single digit increases over the past three days.
"This is a contained cluster. But it is our biggest one. And that means the tail will be long, and the cases will keep coming for a while to come," Ardern told reporters in Wellington.
To maintain control as Auckland eases down to Level 2 restrictions, which will allow schools and shops to reopen, public gatherings will still be restricted to a maximum of 10 people, Ardern said.
The rest of the country will remain at Level 2 restrictions, but with the broader limit of up to 100 people at public gatherings. Both situations will be reviewed before Sept. 6, she said.
New Zealand, which has a population of 5 million, has so far recorded just over 1,300 COVID-19 cases, including 22 deaths.
AUSTRALIAN OUTBREAK SLOWS
Meanwhile, neighbouring Australia reported its lowest one-day rise in new coronavirus infections in almost two months on Monday, fuelling optimism that a deadly second wave is subsiding.
Victoria, New South Wales and Queensland and Western Australia states reported a combined 121 new cases over the past 24 hours, the lowest single-day rise since July 5.
Victoria accounted for the vast majority with its capital city of Melbourne the epicentre of the latest outbreak. Victoria earlier this month reported a record 700 cases in a single day.
"It's a light at the end of the tunnel," Australia's Deputy Chief Medical Officer Nick Coatsworth told reporters in Canberra. "It's a substantial reassurance that the overall trend is down."
Australia has recorded nearly 25,000 COVID-19 infections, including 517 deaths.