WELLINGTON (REUTERS, AFP) - New Zealand Prime Minister Jacinda Ardern on Monday (Sept 21) lifted all coronavirus restrictions across the country, except in second-wave hotspot Auckland, as the number of new infections slowed to a trickle.

Some restrictions were also eased in Auckland to allow gatherings of up to 100 people, but the country's biggest city needed more time before all curbs could be lifted, Ms Ardern said.

"Our actions collectively have managed to get the virus under control," she told reporters in Auckland. "This was the centre of the outbreak and that's why that caution is needed here."

Ms Ardern said elimination was still New Zealand's target.

"Analysis completed for the ministry of health suggests that by the end of this month, there is still a 50-50 chance of having eliminated Covid once again," she said.

But she said Auckland "needs more time" to eliminate a stubborn cluster of infections that was detected last month in the city of 1.5 million.

New Zealand, a nation of five million, appeared to have halted community transmission of Covid-19 earlier this year, but the fresh outbreak in Auckland in August prompted the government to place the city back in lockdown.

The origin of the Auckland cluster remains unknown, but health authorities say it is not the same strain of the virus experienced earlier this year.

Despite the mystery, Ms Ardern said extensive testing and effective contract tracing were keeping it contained.

Auckland's alert will move down slightly from 2.5 to two on Wednesday, meaning the maximum number at social gatherings increases from 10 to 100.

The city's virus setting will be reviewed in two weeks, with the possibility it could join the rest of the country at level one on October 7.

The country recorded no new cases of Covid-19 on Monday, keeping its total number of confirmed cases at 1,464, with 25 deaths, far below many other countries.

Ms Ardern, who faces a general election on Oct 17, said a health ministry analysis indicated there was still only a 50-50 chance of having eliminated Covid-19 by the end of the month, maintaining the need for vigilance.

The 40-year-old prime minister has a strong lead over her rivals in the polls due to her success in containing Covid-19.

She was criticised by opposition National Party leader Judith Collins on Monday for taking a group selfie with supporters while campaigning, without maintaining social distance.

Ms Ardern acknowledged it was a mistake.

"I should have stepped further forward, I should have asked them to step apart from each other, and I acknowledge that," she said.