The white supremacist terrorist who callously shot and killed 50 people in a disgusting attack on two mosques in Christchurch, New Zealand, was bullied as an overweight child, friends have said.

Brenton Tarrant, 28, used semi-automatic weapons to kill defenceless Muslims as they prayed at Al Noor and Linwood mosques on Friday. He live-streamed the 16-minute-long brutal onslaught on Facebook.

Fifty people have died and dozens more are being treated in hospital after the shootings - with 12 still in a critical condition.

Tarrant grew up in the north-eastern NSW town of Grafton.

Many of his childhood friends still living in the area have revealed Tarrant was a loner for most of his life.

Tarrant grew up in the north-eastern NSW town of Grafton, and his childhood friends still living there said he was a loner for most of his life. He played for the Grafton Ghosts under 15 rugby league team in 2005 (Tarrant is pictured top left)

Tarrant (pictured as a teen) will never comprehend the impact the alleged attacks have had against his parents in their hometown of Grafton, his cousin said

Many of his childhood friends still living in the area have revealed Tarrant (pictured as a child with his father) was a loner for most of his life

Daniel Tuite played for the Grafton Ghosts under-15 rugby league team with Tarrant in 2005.

Mr Tuite said he went out of his way to speak to Tarrant as he was 'picked on pretty badly'.

'Grafton can be a pretty harsh place... so if you're overweight and a bit what some people might call useless on the field, you're going to probably get picked on. That's why he just kept himself to himself,' Mr Tuite told The Australian.

'Where we're from, we'd never even come in contact with Muslims, really.'

Mr Tuite said Tarrant suffered a knee injury, leading him to spend more time lifting weights at gyms.

'Something just changed and he got really serious about exercise and got himself in shape,' Mr Tuite said.

Tracey Gray, the owner of Big River Gym in Grafton, said Tarrant worked as a personal trainer at the gym five or six years ago.

'He started coming to my facility as a boy that was finishing school and showed a lot of dedication to his own training. Then he went and did his personal training qualifications,' she told Stuff.

Tarrant's grandmother, Marie Fitzgerald, said Tarrant also spent time 'learning the ins and outs of computers and playing games on computers' during his youth.

Other relatives, including Tarrant's grandmother Marie Fitzgerald and uncle Terry Fitzgerald (pictured) broke their silence on Sunday

Mrs Fitzgerald said she was still coming to grips with what had happened.

'It's just so much of everything to take in that somebody in our family would do anything like this,' the 81-year-old woman told Nine News.

'The media is saying he has planned it for a long time so he is obviously not of sound mind.'

The last time Tarrant returned home to NSW was for his sister's birthday last year.

Tarrant's cousin Donna Cox said it 'hurts' to be related to the alleged mass-murderer.

The 28-year-old faced court on Saturday, smirking and giving a white supremacist sign as he was charged with one count of murder.

Ms Cox said Tarrant would never comprehend the impact of his actions on his family.

'That he is from... a very respected family, his mum, his dad, were pretty high in the community here,' she told Sunday Night.

'He wasn't raised like that, but I'm not here to defend him. If I could ask him - I'd ask him why. How could you do that?

Tarrant's grandmother, Marie Fitzgerald (pictured), said Tarrant also spent time 'learning the ins and outs of computers and playing games on computers' during his youth

Christchurch mosque shooter Brenton Tarrant grew up in this house in Grafton, New South Wales

'That's a twisted mind right there. You'd have to be to be able to do something like that.'

She said Tarrant should receive the death penalty for his actions.

Tarrant's mother, Sharon, is a teacher at a local school. She had to be whisked away by police mid-class when reports of the attack first came through on Friday.

She and Tarrant's sister, Lauren, have been placed under police protection, without mobile phone contact with the rest of their family.

Cousin Donna Cox (pictured) says she is in disbelief over the attacks, and that accused gunman Brenton Tarrant should be given the death penalty

As a child, Tarrant was obsessed with guns and violent video games, Ms Cox said.

His father, a local garbageman who died from cancer in 2010, was widely-liked in the community.

After his father's death, Tarrant began travelling around Europe. Bulgarian and Turkish authorities are investigating his travel history, determining whether he had ulterior motives for frequenting their countries over the span of seven years.

Somewhere along his journeys, he allegedly forged extremist views and a hatred for non-white immigration, feelings that culminated in Friday's attacks.

Tarrant will re-appear in New Zealand's High Court on April 5, when additional charges are expected to be laid.