New Zealand has spent 20 days in lockdown to fight a Delta variant outbreak, first identified by a single case on August 17.

From a peak of 83 cases on Sunday, August 29, cases have slipped to 20, recorded on each of the last three days.

"We are making progress," Ms Ardern said.

That progress will see around 3.4 million Kiwis lifted out of lockdown from Wednesday.

While Ms Ardern's cabinet has opted to keep Auckland - the centre of the outbreak - in a level four lockdown for at least another week, the rest of New Zealand will take a step closer to normality.

Places outside of NZ's biggest city will shift from level three, a lesser lockdown, to level two, which allows Kiwis to return to work and school, and removes most restriction from business.

"Moving to level two is progress and it is positive but it comes with a warning," Ms Ardern said.

"We're within sight of elimination but we cannot drop the ball."

New Zealand has been mocked by Australian politicians, including Prime Minister Scott Morrison and NSW Premier Gladys Berejiklian for its pursuit of an elimination strategy.

While a return to zero case days appears feasible, Ms Ardern cautioned against complacency - urging compliance with COVID-19 rules and increased community testing.

"If we continue to make progress we will get back to a level one environment," Ms Ardern said.

"I would rather get (to zero cases) and declare that's what we've achieved than get too far ahead of ourselves.

"There is work to be done.

"Today, we've got one case ... they're in a large household so almost inevitably you'll see extra cases come through from that.

"So it's day by day. But day by day we are making very good progress."

In a likely reference to Australia, she said "what I don't want to do is make the mistake of moving too quickly and then seeing a resurgence because that has happened with Delta before."

Citing the greater infectiousness of the Delta variant, Ms Ardern's goverrnment has tweaked level two rules from their previous operation.

A mask-wearing mandate will apply to almost all indoor venues.

Checking in at venues will also become mandatory in an effort to aid contact-tracing in the event of future outbreaks.

A new limit of 50 people will apply to many indoor venues to reduce super-spreading events.

Gyms and other public facilities must also provide spacing of two metres between patrons.

Auckland remains by a distance New Zealand's hardest-hit city through the pandemic, notching 102 days in total under lockdown conditions on Monday.

All of Monday's 20 cases were identified in Auckland, which is home to 804 of the 832 total infections in this outbreak.

The level four rules put 1.7 million Aucklanders in harsh lockdown conditions, with no gatherings permitted, very few reasons to leave households and major curbs on business.

There are 40 people with COVID-19 in hospital, and six in intensive care units.

New Zealand's COVID-19 death toll is 27, after a woman aged in her 90s, died after contracting the virus last weekend.

Australian Associated Press