A knife-wielding attacker stabbed five people in a New Zealand supermarket Monday, critically injuring three, but Prime Minister Jacinda Ardern said it appeared the rampage was not terror related.

Police said the attack -- highly unusual in the normally peaceful South Pacific nation -- occurred at a Countdown supermarket in central Dunedin at 2:30pm (0230GMT) and a man had been taken into custody.

Witnesses told local media a man carrying two knives stabbed staff in the supermarket and bystanders who tried to stop him were also injured.

The most recent mass-casualty attack in New Zealand was the Christchurch mosques shootings in March 2019, when a white supremacist gunman murdered 51 Muslim worshippers and severely injured another 40.

Ardern said the first question she asked police was whether the Dunedin attack had national security implications but they assured her it did not.

"At this stage, there's nothing to suggest from the police's perspective that this is what they would define as a domestic terror event," she told reporters.

Ardern also said police were not looking for anyone else in relation to the attack.

"I want to acknowledge early reports of bystanders who have taken action in order to protect those around them... these are courageous acts and we are thinking of the families," she said.

Countdown's managing director Spencer Sonn said everyone at the supermarket chain was "shocked and devastated" by the attack.

New Zealand introduced tough gun laws in the wake of the Christchurch attack to limit access to firearms.