Heavily armed officers remain at Lynnmall following the attack at a Countdown supermarket in New Lynn, a southwest suburb of Auckland, on Friday afternoon.
St John say three patients are in a critical condition at Auckland City Hospital.
A further three patients - one in a serious condition and two in moderate conditions - have also been taken to hospitals across Auckland.
Police said a man entered the supermarket and injured multiple people, before he was located and shot by police.
The man died at the scene, according to police.
Frightening first-hand reports of the attack are emerging.
Newshub reports Amit Nand was at the supermarket during the attack.
"People were running up to me saying 'go outside because people are being stabbed' ... I saw him with a knife," he said.
"I went past him, I went by him with another guy and I told him to 'drop the f***ing knife."
Mr Nand says he was then approached by an undercover cop.
"The cop is like 'get back' and he started shooting him five times and killed him."
Michelle Miller, a resident of nearby Avondale, told Radio NZ she saw a man "running around with a knife, then he just lost the plot".
"It's horrific. I feel sorry for the Countdown staff, I feel sorry for the people who were actually hurt here today," she said.
"The police have done an amazing job. They had the guy try to give himself up but he wouldn't. It's really sad that they had to do what they had to do."
Countdown spokeswoman Kiri Hannifin said staff were "devastated" by the attack.
"Our hearts are heavy knowing what our team and customers have witnessed and been through," she said in a statement.
New Zealand is currently in a national lockdown to fight a COVID-19 outbreak, with Auckland at strict level four settings.
The attack is New Zealand's second supermarket stabbing this year, after a May incident at a Countdown store in Dunedin which left four people injured.
AAP with The Project.