New Zealand Prime Minister Jacinda Ardern speaks at a press conference. File photo

New Zealand's largest city Auckland will remain in a coronavirus lockdown for at least another two weeks but some restrictions will be eased slightly from Wednesday, Prime Minister Jacinda Ardern told a news conference on Monday.

The city, which is at the centre of the latest Delta variant outbreak, will move to alert level 3 from alert level 4 starting midnight on Tuesday as the cluster has been concentrated in Auckland and the rest of the country moved out of lockdown earlier this month.

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Schools and offices will still remain closed at level 3 but businesses can operate contactless services.

The rest of the country will remain at alert level 2, she said.

A medical worker administers a virus test during a lockdown in Auckland. File/Reuters

Ardern said the city of two million would move down to level three on New Zealand's four-tier coronavirus response system by late Tuesday, even as authorities remain committed to eliminating a Delta-variant outbreak.

"We're moving now because the advice we have is that we do not have widespread, undetected transmission in Auckland," she told reporters.

"If everyone continues to play their part, we can continue stamping out (the virus)."

The change means stay-at-home orders will remain in place but some businesses, such as takeaway food outlets, can open using contactless delivery.

New Zealand imposed a nationwide lockdown on August 17 when the first case of the highly transmissible Delta variant was found in the community.