Police said the suspect was also injured and was being treated in police custody for his injuries. Police expect him to be charged later Monday.
Those in the store at the time told local media that it was a confusing scene, with some screaming and running towards the exit, while others rushed to help.
Prime Minister Jacinta Artern said the motive for the attack had not been established, but police had no evidence to suggest it was domestic terrorism.
“Needless to say, an attack like this is huge, and I would like to acknowledge the early reports of the courageous actions of the audience who took action to protect those around them,” Artern said. “Our thoughts are with everyone affected by this attack.”
Artern said five people were taken to Dunedin Hospital with stab wounds or related injuries.
Health officials said three of the injured had been admitted to the intensive care unit at Dunedin Hospital.
“We are shocked by what happened at our Dunedin Central store this afternoon,” Countdown said in a statement. “Now our priority is to take care of our injured team members and our broader team in the aftermath of this very traumatic event. We are deeply saddened by the injuries of customers who tried to help our team members.”
About 130,000 people live in Dunedin, including a large number of students who studied at the University of Otago.
Nick Perry, The Associated Press