The sentencing of an Australian white supremacist who killed 51 Muslim worshippers in New Zealand and live-streamed the massacre on Facebook is set to begin on Monday.

Tight security is around a court in Christchurch, where Brenton Tarrant, the shooter, will hear statements from 66 survivors.

The court building was sealed off with large orange barriers as armed police stood guard.

Lawyers expect Tarrant to be the first person to be jailed for life without parole in New Zealand.

The hearing is set for four days with survivors and Tarrant making submissions before High Court judge Cameron Mander announces his sentence.

Tarrant is representing himself and is reportedly being held in a cell deep within the court complex to avoid transporting him to and from jail.

On March 15th, 2019, he armed himself with a semi-automatic rifle and stormed into two mosques and opened fire on worshippers at Friday prayer.

He was quickly arrested and initially pleaded not guilty to 41 murders, 40 attempted murders and committing a terrorist act.

In March 2020, he changed his plea to not guilty.

Prominent Christchurch lawyer Nigel Hampton said the "terrifying" crime probably "needs an extraordinary sentence", while law professor Chris Gallavin said "he'll never see the light of day again". 

Judge Mander has said the sentencing process was important for the victims, and "finality and closure is considered by some as the best means of bringing relief to the Muslim community". 

Prime Minister Jacinda Ardern has said that this week would be difficult for many.

"I don't think there's anything I can say that is going to ease how traumatic that period is going to be," she told reporters. 

Increased police will be around the courthouse and victim support workers will also be present. Local mental health specialists will also be on standby for referrals.