New Zealand reported 28 new cases of COVID-19 on Friday, a big drop compared to the last few days, as authorities said the country was breaking the chain of transmission of the highly infectious Delta variant of coronavirus.

Authorities said 27 new cases were in Auckland and one was in Wellington. Friday's numbers were lower than 49 new cases reported on Thursday and 75 the day before.

"While the fall is encouraging we are mindful these outbreaks can have a long tail...," Director of Public Health Dr Caroline McEnlay said in a news conference.

"We are being successful in breaking the chain of transmission," she said.

Barring a few cases in February, New Zealand had been largely free of coronavirus until the Delta outbreak prompted Prime Minister Jacinda Ardern to order the snap lockdown last month.

About 1.7 million people in the largest city of Auckland still remain in strict level 4 lockdown. Curbs have been eased in the rest of the countries but schools and offices as well as cafe, restaurants and all public venues remain shut. Most New Zealanders have been asked to stay indoors.

Ardern's lockdowns and international border closure since March 2020 have been credited with reining in COVID-19, largely freeing up day-to-day activities from curbs.

But the government faces questions over a delayed vaccine rollout that has left a majority of the population exposed to the latest outbreak.

Just over a quarter of New Zealand's 5.1 million people have been fully vaccinated, the slowest pace among the wealthy nations of the OECD grouping.

New Zealand has reported 3,372 cases of COVID-19 since the pandemic began and 26 related deaths.