New Zealand Prime Minister Jacinda Ardern has announced new restrictions requiring travellers to be quarantined for 14 days upon entry into the country in an attempt to stop the spread of coronavirus.

Key points: Jacinda Ardern calls the restrictions the "toughest border restrictions of any country in the world"

Jacinda Ardern calls the restrictions the "toughest border restrictions of any country in the world" All cruise ships are banned from going to New Zealand until June 30

All cruise ships are banned from going to New Zealand until June 30 A memorial service for the Christchurch massacre has also been cancelled

The restrictions apply to all countries except for Pacific nations, and will come into effect at midnight on Sunday (10.00pm AEDT). It also includes any New Zealand citizens or residents returning to the country.

New Zealand has six confirmed cases and no recorded deaths.

Ms Ardern said these were "far-reaching and unprecedented" measures to tackle a global pandemic.

"Alongside Israel and a small number of Pacific islands who have effectively closed their borders, this decision will mean New Zealand will have the widest ranging and toughest border restrictions of any country in the world," Ms Ardern said.

"We are also encouraging New Zealanders to avoid all non-essential travel overseas. This helps reduce the risk of a New Zealander bringing COVID-19 back with them."

Ms Ardern also announced a ban on cruise ships coming to New Zealand.

"As of midnight tonight, we're issuing to all cruise ships not to come to New Zealand until at least June 30, that is for incoming cruise ships, at which time the directive will be reviewed," she said.

The news will have implications for a number of Australian sporting leagues and events, and already the remaining two games of Australia's three-match ODI series with New Zealand have been called off, as well as Australia's upcoming tour of the country.

Christchurch memorial called off

Meanwhile, Christchurch families will be forced to mourn the 51 people killed in last year's mosque shooting in isolation after a national memorial service was cancelled due to coronavirus fears.

In a statement, Ms Ardern said while New Zealand had no cases of human-to-human transmission of COVID-19, the event was called off as a precaution.

"This a pragmatic decision," she said.

"We're very saddened to cancel, but in remembering such a terrible tragedy, we shouldn't create the risk of further harm being done."

New Zealand Government Minister Megan Woods said medical authorities raised concerns about the public nature of the memorial service, scheduled to be held an arena in Christchurch's outskirts.

Travellers from across and outside the country were expected to gather and because it was non-ticketed, traceability of attendees became a concern.

The cancellation of the memorial service was received with mixed feelings.

It is not typical in Islamic culture to hold memorial or anniversary days — prayers for the dead are made every day for Muslims.

A large crowd was expected to gather at Sunday's memorial service. ( ABC News: Brendan Esposito )

However, one of the widows scheduled to speak at the service said while public health takes precedence, she was disappointed the event was called off.

Dr Hamimah Tuyan's husband was the 51st person to die in the Christchurch mosque attacks — she was in Singapore at the time and watched the horrific shooting unfold over Facebook and YouTube.

"It doesn't just affect widows, it has affected [dozens of injured] people and people who were mentally traumatised," she said.

"It has affected the whole nation."

She said everyone had to embrace differences and hold onto commonalities.

"So we [Muslims] have to do the same thing that we ask others to do with us," she said.

The two mosques involved in the shooting, Al Noor and Linwood, will be restricting access to family and community members on Sunday.

The sites also increased their security detail after death threats made towards worshippers were posted to an encrypted messaging service two weeks ago.

The threat, posted on a channel dedicated to the Australian gunman, led to the arrest of a 19-year-old man who was understood to have connections to a local white supremacist group.

Over the past week, the mosques have seen an influx of visitors from across New Zealand.