New Zealand Prime Minister Jacinda Ardern welcomed the life sentence for the Christchurch mosque gunman on Thursday (Aug 27), saying Brenton Tarrant deserved a lifetime of "complete and utter silence".

The March 2019 attacks targeting people praying at the Al Noor and Linwood mosques shocked New Zealand and prompted new laws banning the deadliest types of semi-automatic weapons.

Judge Cameron Mander imposed the maximum available sentence on the 29-year-old Australian gunman, the first time the sentence has been imposed in the country.

The judge said the crimes were so wicked that a lifetime in jail could not begin to atone for them.

During the four-day sentencing hearing, 90 survivors and family members recounted the horror of the attacks and the trauma they continue to feel.

Ardern praised the "strength" of the country's Muslim community following the sentencing.

"Nothing will take the pain away, but I hope you felt the arms of New Zealand around you through this whole process," she said.

"The trauma of Mar 15 is not easily healed but today I hope is the last where we have any cause to hear or utter the name of the terrorist behind it," said Ardern, who was widely praised for her response to the attacks last year that killed 51 Muslim worshippers.

"His deserves to be a lifetime of complete and utter silence", Ardern said.