New Zealand police arrested two people Thursday over online threats against two Christchurch mosques targeted in a white supremacist attack two years ago that claimed the lives of 51 Muslims.

Police in the South Island city said an online threat was made earlier this week against the Al Noor mosque and the Linwood Islamic Centre, which were targeted in New Zealand's most deadly shooting in 2019.

No information about the nature of the threat was supplied and neither suspect has been named. No charges have yet been laid, police said, according to remarks carried by Agence France-Presse (AFP).

"We take all threats of this nature seriously and we are working closely with our Muslim community," said Canterbury District Commander Superintendent, John Price in an emailed statement. "Any messages of hate or people wanting to cause harm in our community will not be tolerated - it's not the Kiwi way."

New Zealand is on heightened alert ahead of the March 15 anniversary of the Christchurch attack. Armed with high-capacity semi-automatic weapons, Australian Brenton Tarrant killed 51 people and injured dozens more after opening fire on worshippers at the two mosques, livestreaming the attacks on Facebook before being arrested.

In August, Tarrant was sentenced to life in prison without parole, the first time New Zealand confined anyone for the rest of their life.

Judge Cameron Mander said the crimes committed by 29-year-old Tarrant were so wicked that a lifetime in jail could not begin to atone for them. He said they had caused enormous loss and hurt and stemmed from a warped and malignant ideology. Tarrant will die in jail under the life sentence.

"Finally justice has been served," said Hina Amir, on the phone from her living room a few suburbs away from the street front of Al Noor mosque where she and her husband Amir Daud survived a hail of Tarrant's bullets in their car.

Together on their lounge, they watched a livestream of three emotional days of sentencing proceedings, as other survivors and relatives confronted Tarrant directly in court and asked he never be released. Outside the courthouse, the sentence was greeted with cheers.

Abdul Alabi Lateef, imam of the second mosque that Tarrant attacked, said justice had been done. Gamal Fouda, imam of Al Noor mosque, where 44 people were slain, said no punishment would bring lost loved ones back.

Tarrant has admitted his crimes and said through his lawyer that he did not oppose the sentence. He made no reaction when it was handed to him in court.