At least 49 people were killed in separate attacks on two mosques in Christchurch on Friday, horrifying New Zealanders.

Former NSW personal trainer Brenton Harrison Tarrant, 28, appeared in a Christchurch court on Saturday where he was formally charged with one count of murder.

Two armed guards escorted Tarrant into the court and he showed no expression as District Court Judge Paul Kellar read one charge of murder to him, the AP reported.

The court appearance lasted only about a minute and he was led back out in handcuffs. He was ordered to return to court again April 5.

After Tarrant left, the judge said that while "there is one charge of murder brought at the moment, it is reasonable to assume that there will be others."

Tarrant did not apply for bail or to have his name suppressed and has been remanded in custody.

The Christchurch Press reported Tarrant was wearing a tunic and was handcuffed.

He did not speak, but was looking around particularly at the media present.

NZ Police closed the Christchurch court to the public over security concerns, but media was able to attend.

Two other people arrested are yet to be charged.

NZ Prime Minister Jacinda Ardern said on Saturday inquires were ongoing to establish whether the other two were directly involved.

A fourth person arrested on Friday was a member of the public who was in possession of a firearm, but with the intention of assisting police, she said. They have since been released.

Tarrant identified himself online as behind the shooting that began as hundreds of worshippers gathered for prayers in the South Island city on Friday.

Tarrant, 28, grew up in Grafton in NSW and stated in a rambling 74-page "manifesto" posted online before the attack he had spent years in planning vengeance for deaths in Europe, before deciding on Christchurch three months ago.

Australian Associated Press