The Australian terrorist who filmed himself slaughtering 50 worshipers at two mosques in New Zealand has asked to represent himself in court, prompting concerns the trial could become a platform to promote his far-Right ideology.

Brenton Tarrant, a white supremacist who gunned down his victims with a semi-automatic rifle at the Al Noor and Linwood mosques in Christchurch, sacked his court-appointed lawyer so he could defend himself.

His former lawyer, Richard Peters, told reporters that the attacker "indicated he does not want a lawyer" and that he "wants to be self-represented in this case."

Mr Peters, who represented Tarrant at a preliminary court hearing, played down speculation that he was mentally unfit to stand trial.

"The way he presented was rational and someone who was not suffering any mental disability. That's how he appeared. He seemed to understand what was going on," Mr Peters said.