CHRISTCHURCH (REUTERS) - The main suspect in New Zealand's worst peacetime mass shooting intended to continue the rampage before he was caught by police, Prime Minister Jacinda Ardern said on Saturday (March 16).

"The offender was mobile, there were two other firearms in the vehicle that the offender was in, and it absolutely was his intention to continue with his attack," Ms Ardern told reporters in Christchurch.

The suspect, identified as Brenton Harrison Tarrant, a 28-year-old Australian citizen, has been charged with murder, though Ms Ardern added that further charges are likely.

"I'm not privileged to a full breakdown at this point but it is clear that young children have been caught up in this horrific attack," she said regarding victims of the attack.

Tarrant appeared in a Christchurch District Court on Saturday and was remanded without a plea until his next scheduled appearance in the South Island city's High Court on April 5.

Handcuffed and wearing a white prison suit, Tarrant did not speak.

His court-appointed lawyer made no application for bail or name suppression.

The attack, which Ms Ardern labelled as terrorism, was the worst ever peacetime mass killing in New Zealand and the country raised its security threat level to the highest.

Tarrant has been identified as a suspected white supremacist, based on his social media activity.