WELLINGTON: New Zealand eased coronavirus curbs slightly in its largest city of Auckland on Monday, as the government expressed confidence that there was no widespread regional transmission of the Delta variant.

But tough restrictions will continue even after midnight on Tuesday, when the alert level drops to 3 from 4 in the city of about 1.7 million at the centre of the latest Delta outbreak.

Schools and offices must still keep closed, for instance, with businesses limited to offering only contactless services.

Residents must still keep to their own "bubbles", cannot visit friends or neighbours, or let children play together, Prime Minister Jacinda Ardern said.

"Bubbles must remain small and exclusive," she told a news conference.

"We are confident that there is no large-scale undetected transmission," Ardern said. "There is ongoing work to stamp it out, which is why we are still at level 3."

The Auckland restrictions will ensure the Delta variant is stamped out as New Zealand sticks with its strategy of elimination of the virus, Ardern added.

Monday's relaxation allows for up to 10 people to attend funerals and weddings, while businesses can offer contactless pick-up or delivery services, including takeaways.

Auckland will stay at level 3 for at least two weeks. For the rest of the country, the level will remain at 2, Ardern said.

New Zealand reported 22 new cases of COVID-19 on Monday, all in Auckland, which has been in a full level-4 lockdown since mid-August. Until then, the country had been largely virus-free. Its tally of infections is 3,725, with 27 deaths.

Ardern's tough lockdowns and international border closure helped rein in COVID-19, but her government has been criticised for a slow rollout of vaccine that exposed much of the population to Delta.

New Zealand has since ramped up its vaccine drive, with purchases of additional vaccine doses from Spain and Denmark.

It still plans a phased re-opening of borders early next year, Ardern has said.