Tarrant, a self-described white supremacist, is being sentenced on 51 counts of murder, 40 counts of attempted murder and one terrorism charge after attacks on two mosques last year.

Alongside the gruesome step-by-step outline of his attacks, it was revealed Tarrant intended to burn down the mosques after killing worshippers inside.

On Monday, victims gathered at the Christchurch High Court after travelling from across the globe, Australia and New Zealand.

Hundreds packed the court room and seven overflow rooms, with hundreds more watching on live streams in 15 nations.

The Grafton-raised killer live-streamed his crimes but pleaded not guilty until March when he reversed his plea.

The 29-year-old was brought into the courtroom by five corrections officers, watching proceedings cross-legged and stony-faced, showing little emotion throughout.

One by one, as 66 people will do over the coming days, his victims detailed their shattered lives and broken hearts, with the terrorist sitting just metres away.

Maysoon Salama, the mother of Ata Mohammad Ata Elayyan who was killed at Al Noor mosque, paid an emotional tribute to her slain son.

"His name means a gift from Allah and he was the best gift to us for 33 years," she said through teary eyes.

"My family and I have been very devastated by the inhumane murder of our precious son.

"Losing my son is like feeling the tight pain of labour again and again."

Like many, Ms Salama eyeballed Tarrant during parts of her address.

"May you get the severest punishment for your evil act in this life," she said.

"You transgressed and you thought you could break us. You failed miserably. We remain stronger in our belief of Islam."

In all, 24 people gave impact statements on Monday, including some who sent pre-recorded videos from abroad and some who allowed victim support workers to give their address on their behalf.

Others took to the microphone, surrounded by family or friends as they gave the hardest speech of their lives.

Muhubo Ali Jama, who met and fell in love with Muse Awale at the same mosque where he was murdered, said she retained sleeping difficulties to this day.

"Since then I have been unable to drive my car. The last time I drove it was to the mosque on the 15th of March. I am too scared ... because of this I have lost my independence," she said.

Ms Jama has also lost her job, her hobbies and has been forced to move house.

"I have lost my husband, my lifelong companion. I could never share the love that we have again," she said.

Mariam Gul lost her entire family, her parents and brother, in the attack.

"There is an emotional void within my family. It is very difficult to believe that all of them has gone in a single incident in a place of safety and prayer, in a mosque," she said.

Before the statements, Crown representative Barnaby Hawes detailed the summary of facts, taking an hour to read a document, which included the means of death of the 51 killed.

At one point, Tarrant roamed the mosque and executed any injured worshippers who showed signs of life - including a toddler who clung from his father's leg who Tarrant killed "with two precisely aimed shots".

Tarrant did not offer resistance upon his arrest, and subsequently confessed his crimes in police interviews, where he also said he regretted not killing more people and not burning down the mosques.

The hearing continues, with Tarrant likely to be given life imprisonment when Justice Cameron Mander hands down his sentence on Thursday.

Australian Associated Press