A woman touches a photo at a memorial site that was set up after the March 2019 shootings [File: Edgar Su/Reuters]

The Christchurch mosque attacker is considering appealing his whole-of-life jail term for the 2019 mass shootings, arguing his guilty pleas were made under duress, his lawyer said on Monday.

Self-proclaimed white supremacist Brenton Tarrant pleaded guilty to 51 charges of murder, 40 of attempted murder and one of terrorism in March last year.

He was sentenced to life imprisonment without the possibility of parole, the first time a whole-life term has been handed down in New Zealand.

Tarrant did not offer a defence at the time, but his lawyer Tony Ellis said the 31-year-old Australian citizen was now questioning his decision to plead guilty.

Ellis said the gunman had told him the pleas were entered under duress because he was subject to “inhuman and degrading treatment” while being held on remand.

“He decided that the simplest way out was to plead guilty,” Ellis told Radio New Zealand.

Armed with semi-automatic weapons, Tarrant attacked Friday worshippers at Christchurch’s Al Noor mosque and Linwood prayer centre in March 2019, livestreaming the killings as he went. His victims were all Muslim and included children, women and the elderly.

Ellis reportedly took over as Tarrant’s lawyer ahead of a coroner’s inquiry into the attacks and advised his client to exercise his right of appeal.

He said Tarrant had given him about 15 pages of detailed descriptions of his alleged mistreatment.

“By this, he means he was subject to inhuman or degrading treatment while on remand, which prevented a fair trial,” Ellis wrote last week in a memorandum to the chief coroner, according to Stuff, a NeIn the note to the coroner, Ellis stressed that every accused or convicted person was entitled to exercise his right of access to the court.

“He was sentenced to over 25 years, that is a sentence of no hope and that’s not allowed, that’s a breach of the Bill of Rights,” Ellis said.

New Zealand does not have the death penalty and in sentencing in August last year, Judge Cameron Mander said he was imposing the harshest possible term for Tarrant’s “inhuman” actions.

“Your crimes are so wicked, that even if you are detained until you die it will not exhaust the requirements of punishment and denunciation,” Mander said at the time.

Ellis declined to comment when contacted by the AFP news agency, saying his client had instructed him to speak only to selected local media outlets.

There was no immediate response from the Coroners Court.

Abdullah Naeem, whose brother and father were killed in the attacks, told Stuff that the convicted killer was “playing games”.

Naeem, who spoke on behalf of the March 15 Whānau Trust, said he hoped the law would stop the appeal going ahead, so families would not have to go through more trauma.

“Life imprisonment is a light punishment for what he did,” he said. “Any good law will deny his plea and I hope that happens.”w Zealand media outlet.