The Australian white supremacist who murdered 51 Muslims in last year's New Zealand mosques shooting showed no emotion as his sentencing hearing opened Monday with horrific details of an atrocity prosecutors said was meticulously planned to inflict maximum casualties.

Brenton Tarrant wanted "to have shot more people than he did", the court was told at the start of the four-day sentencing, held amid tight security and in front of bereaved families and wounded survivors.

A police officer outside Al Noor mosque
A police officer stands guard outside the Al Noor mosque ahead of the first anniversary of the Christchurch mosque shootings in Christchurch in March 2020. Photo: AFP / Sanka VIDANAGAMA

The court heard how the heavily-armed Tarrant opened fire on men, women and children as he live-streamed the attack on social media, ignoring pleas for help, and driving over one body as he moved from one mosque to the next.

When he saw a three-year-old clinging to his father's leg, Tarrant shot him "with two precisely aimed shots," prosecutor Barnaby Hawes told the court.

Christchurch shooting
The twin mosque massacres prompted outpourings of grief from much of New Zealand. Photo: AFP / Anthony WALLACE

Tarrant has pleaded guilty to 51 charges of murder, 40 of attempted murder and one of terrorism over the attacks on two mosques in Christchurch in March last year.

Lawyers expect the 29-year-old to be the first person jailed for life without parole in New Zealand.

Police officers secure outside Christchurch high court
Police officers secure the area outside the Christchurch High Court ahead of the sentencing of the Australian white supremacist Brenton Tarrant in Christchurch. Photo: AFP / Sanka VIDANAGAMA

Tarrant was arrested as he drove to attack a third mosque in Ashburton, about an hour south of Christchurch.

Wearing grey prison clothing and surrounded in the dock by three police officers, the Australian remained silent, occasionally looking around the room, as Hawes delivered a chilling summary of facts, and members of the Muslim community recounted the impact on their lives.

Survivors of Christchurch mosque attack
Survivors and family members of Christchurch mosque attacks victims arrive outside the Christchurch High Court. Photo: AFP / Sanka VIDANAGAMA

"He admitted (to police) going into both mosques intending to kill as many people as he could," Hawes said.

"He stated that he wanted to have shot more people than he did and was on the way to another mosque in Ashburton to carry out another attack when he was stopped," he said.

Police stands guard at Christchurch court
An armed police officer stands guard outside the Christchurch High Court. Photo: AFP / Sanka VIDANAGAMA

"In his interview, the defendant referred to his attacks as 'terror attacks'.

"He further stated the attacks were motivated by his ideological beliefs and he intended to instil fear into those he described as 'invaders' including the Muslim population or more generally non-European immigrants."

Sentencing of Australian begins in Christchurch court
The sentencing of an Australian white supremacist who killed 51 Muslim worshippers in New Zealand -- and live-streamed the massacre -- begins amid tight security in a Christchurch court. Photo: TVNZ

Abdiaziz Ali Jama, a 44-year-old Somali refugee, saw her brother-in-law Muse Awale shot dead, and said she continued to suffer mental trauma.

"I see the images and I hear the constant sound rata-rata-rata -- the sound of the gun shooting -- in my head," said Jama, echoing the words of several speakers.

"I have flashbacks, seeing dead bodies all around me. Blood everywhere," added a son of Ashraf Ali.

Gamal Fouda, the Al Noor mosque Imam, said he was standing in the pulpit "and saw the hate in the eyes of a brainwashed terrorist" before telling Tarrant: "Your hatred is unnecessary."

The court was told Tarrant arrived in New Zealand in 2017 and based himself in Dunedin, 360 kilometres (220 miles) south of Christchurch, where he built up a collection of high-powered firearms and purchased more than 7,000 rounds of ammunition.

He also bought military-style ballistic armour and tactical vests.

Two months before the attack, he drove to Christchurch and flew a drone over the al Noor mosque, filming the grounds and buildings, including entries and exits and made detailed notes about travelling between mosques.

On Friday, March 15 2019 he left his Dunedin address and drove to Christchurch armed with a range of high-powered weapons on which he had written references to historic battles, figures of the Crusades and more recent terror attacks and symbols.

He had ammunition pre-loaded into magazines, as well as modified petrol containers "to burn down the mosques and said he wished he had done so," Hawes said.

Dressed in military-style camouflage clothing including a full tactical vest with the front pockets containing at least seven fully loaded magazines and a scabbard holding a bayonet-style knife, he mounted a camera on his helmet to record the attacks.

Tarrant is representing himself at the hearing. Judge Cameron Mander has imposed reporting restrictions to prevent his using the court as a platform for extremist views.

Mander is expected to hand down a sentence on Thursday.

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