CHRISTCHURCH - Australian Brenton Tarrant appeared in a New Zealand court on Friday where the suspected white supremacist was charged with an additional 49 counts of murder at two mosques last month.

In an attack broadcast live on Facebook, a lone gunman armed with semi-automatic weapons targeted Muslims attending Friday prayers in Christchurch on March 15, killing 50 worshippers and wounding dozens of people.

Tarrant, who was charged with one murder a day after the shooting attack, was also charged with 39 attempted murders on Friday.

The High Court judge overseeing the appearance ordered Tarrant to undergo a mental assessment to determine whether he was fit to stand trial. He was not required to submit a plea.

Tarrant, 28, has been moved to New Zealand's only maximum-security prison in Auckland and appeared at the Christchurch High Court through a video link.

Tarrant was then remanded to custody until June 14.

High Court Judge Cameron Mander said whether Tarrant would be required to enter a plea at his next appearance depended on his mental health assessment and "any other developments".

Legal experts said two mental health experts would likely assess Tarrant, while police, who have not ruled out further charges, would continue to investigate New Zealand's worst peacetime mass killing.

Prison officials say Tarrant is under 24-hour surveillance with no access to media, according to news reports.

He appeared via video handcuffed and seated, wearing a grey prison t-shirt. He listened calmly throughout the hearing, which lasted roughly 20 minutes.

Around two dozen family members of victims and some survivors of the attacks were present in the courtroom.

"The man had no emotion," said Tofazzal Alam, a regular at one of the mosques, when asked about seeing the suspect on video.

Tarrant would be represented by two Auckland lawyers, one of them, Shane Tait, said in a statement on his website, which did not include any comments on the case.

Tait on Friday said he was arranging for his client to receive psychiatric assessment and that the process would take "some months", according to court minutes.