The mother and sister of a man charged with murdering worshippers at two mosques in New Zealand are in a safe house, while relatives in NSW have said sorry to the victims.

Terry Fitzgerald, the uncle of Brenton Tarrant, has apologised to the families of the victims in the terrorist attacks allegedly committed by his nephew.

"We are so sorry for the families over there, for the dead and the injured. What he has done is just not right," Mr Fitzgerald said on behalf of his family to Nine News on Sunday.

The apology came as Tarrant's grandmother Marie Fitzgerald revealed Tarrant's mother and sister had been taken to a safe place for their protection.

"The police will do their duty and keep them protected which is what they need and no phone contact, they have said you can't contact them," the 81-year-old woman said.

Mrs Fitzgerald said the family was "gobsmacked" to have learned Tarrant had been charged with murdering Muslims at mosques in Christchurch.

"It's just so much of everything to take in that somebody in our family would do anything like this," she said in the NSW town of Grafton.

Tarrant reportedly went to Europe after his father died of cancer in 2010 and came back a different man, Mrs Fitzgerald said.

"It's only since he travelled overseas I think that, that boy has changed completely to the boy we knew," Mrs Fitzgerald said.

Tarrant will be prosecuted in New Zealand over the Christchurch mosque attacks that killed 50 people.