WELLINGTON (REUTERS) - The man who killed 51 people at two mosques in New Zealand in 2019 looked his surviving victims and their families in the eye on Monday (Aug 24) as they recounted the horror of a massacre which prosecutors said he carefully planned to cause maximum carnage.

Australian Brenton Tarrant, 29, has pleaded guilty to 51 murder charges, 40 charges of attempted murder and one charge of committing a terrorist act in relation to the massacre in the city of Christchurch which he livestreamed on Facebook.

He could be the first person in New Zealand to receive a term of life in prison without parole, when a High Court judge sentences him later this week for carrying out the deadliest shooting in the country's history on March 15 last year.

Handcuffed and dressed in grey prison clothes, Tarrant sat with hands clasped for most of the morning's proceedings. He showed little emotion, and looked directly at those delivering victim impact statements.

The mother of Mr Ata Elayyan, who was slain in the shootings, told the hearing that losing her son was like feeling the pain of labour all over again.

Madam Maysoon Salama, speaking just metres away from Tarrant, said she constantly wondered what her son was thinking in his last moments "armed only with his courage" after he was gunned down at the Al Noor mosque on March 15 last year.

"I can't forgive you... you gave yourself the authority to take the souls of 51 people. Our only crime in your eyes is that we are Muslims," she said.

"You killed your own humanity and I don't think the world will forgive you for your horrible crime. May you get the severest punishment for your evil act in this life, and hereafter."

Mr Elayyan, a 33-year-old goalkeeper for the New Zealand men's futsal team, was near the back of the mosque while his father, near the front, survived the attack despite being shot in the head and shoulder.

Mr Gamal Fouda, imam of Al Noor mosque, told Tarrant that he was "misguided and misled" and that his hatred was unnecessary.

"I can say to the family of the terrorist that they have lost a son and we have lost many from our community too," Mr Fouda said. "I respect them because they are suffering as we are."

Tarrant will be allowed to speak at some point during the hearings, although Justice Cameron Mander has powers to ensure the High Court is not used as a platform for extremist ideology.

The attacks prompted a global outpouring of grief as well as scrutiny, with regulations imposed on online platforms after the then 28-year-old livestreamed the mosque shootings shortly after uploading a manifesto.

Crown prosecutor Barnaby Hawes said Tarrant told police after his arrest that he wanted to create fear among the Muslim population.

Tarrant had also expressed regret for not taking more lives and revealed that he had intended to burn down the Al Noor mosque after the shootings, Mr Hawes said.

"He intended to instil fear into those he described as invaders, including the Muslim population or more generally non-European immigrants," Mr Hawes said.

Tarrant fired "two precisely aimed shots" at three-year-old Mucaad Ibrahim who was clinging to his father's leg, Mr Hawes said. Ibrahim was the youngest victim of the shootings.

The shooter spent years purchasing high-powered firearms, researched mosque layouts by flying a drone over his primary target, and timed his March 15 attacks to maximise casualties, the prosecutor said.

While most of Tarrant's victims were at Al Noor mosque, he attacked a second mosque before being detained en route to a third.

Security was tight outside the court, with police dogs pacing the streets and snipers on rooftops, television footage showed.

With social distancing measures in place due to the re-emergence of coronavirus in New Zealand, a small public gallery was at the main court, with survivors and families of victims viewing the proceedings in seven overflow court rooms.

Live reporting from the courtroom was banned, and other restrictions had been put in place on what the media could report.

High Court judge Cameron Mander said that he had received more than 200 victim impact statements, along with submissions from various organisations.

"I have read them all," said Mr Mander, who added that he would not sentence Tarrant before Thursday morning after survivors and family members of victims had an opportunity to address the court.

A murder conviction carries a mandatory sentence of life in prison. The judge can impose a life term without parole, a sentence that has never been used in New Zealand.

The hearings were adjourned until Tuesday morning.