New Zealand has cancelled a national remembrance service to mark Sunday's first anniversary of the Christchurch mosque attacks because of coronavirus fears, Prime Minister Jacinda Ardern said.

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

The service to mark the March 15 mass shooting, when a self-avowed white supremacist opened fire at two mosques during Friday prayers, killing 51, had been expected to attract several thousand people, with many travelling from overseas.

Ardern said New Zealand needed to take a precautionary approach.

"The advice we received for this event is that based on people travelling from different parts of the country and from overseas, if there was a case, it could be difficult to trace those who had come into contact with that person, so we are taking a cautious approach," she said.

"March 15 now becomes an opportunity for every New Zealander to reflect in their own way on the events of a year ago."

The unveiling of a remembrance plaque, also planned for Sunday morning at Christchurch's main al-Noor mosque, has been postponed as a precautionary measure.

Mosque spokesman Tony Green said they had taken the advice of health professionals and it was right not to go ahead with the two remembrance services.

"It would be unwise not to take health advice on coronavirus. It's very concerning," he said.

"It would only need one person to be infected and it would be very difficult to track where the carrier travelled from."

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Six people have so far tested positive for the new coronavirus in New Zealand although there have been no reported cases in Christchurch.

The alleged mosque attacker Brenton Tarrant, an Australian national, is due to go on trial on June 2 facing terrorism charges plus 51 counts of murder and 40 of attempted murder over the killings.