A “violent extremist” has been shot dead by police after injuring six people in a stabbing rampage in an Auckland supermarket.

Three of the victims suffered life-threatening injuries in the terrifying attack in a supermarket in the Auckland suburb of New Lynn on Friday afternoon.

NZ Prime Minister Jacinda Ardern described the man as a terrorist motivated by “violent ideology and ISIS”.

“This was a violent attack. It was senseless and I am so sorry it happened,” Ms Ardern said.

Staff comfort each other outside the supermarket after Friday’s frightening attack. Photo: Getty

She said the man, whose name and age have not been released, was known to police and was under constant surveillance, including at the time of the attack.

“The police surveillance team and special tactical group who were part of that monitoring and surveillance shot and killed him in the space of roughly 60 seconds of the attack starting,” she said.

The man lived in Glen Eden, in Auckland’s west. He had been on a terror watch list since 2016, Ms Ardern said.

Police did not intervene before the man injured six people because they thought he was merely on a regular shopping trip in locked-down south-west Auckland.

Many details about the Sri Lankan national are under court-ordered suppression, Ms Ardern said.

“I can tell you that agencies were using every single possible means available to them to protect the New Zealand public from this individual. Every single possible means,” she said.

She condemned the deadly attack.

“What happened today was despicable, it was hateful, it was wrong,” she said.

“It was carried out by an individual, not a faith, not a culture, not an ethnicity, but an individual person who was gripped by ideology that is not supported here by anyone or any community.”

Frightening first-hand reports have emerged in the hours since the attack.

Newshub reports Amit Nand was at the supermarket when the man struck.

“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 said he was then approached by an undercover police officer.

“The cop is like ‘get back’ and he started shooting him five times and killed him.”

One man told NZ’s 1 NEWS he was alerted to the incident by a phone call from his wife, who works at the Countdown supermarket.

She described scenes of chaos, and hearing loud bangs.

“It was chaos – absolute chaos. So many bangings, like food was down, cans was dropping on the floor, so much noise. All she said to me was someone got stabbed,” he said.

He said she was safe, but understandably shaken.

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.

Earlier, St Johns ambulance told Reuters six people had been injured in the supermarket and taken to hospital. Three were in a critical condition, while one was in a serious condition and two in a moderate condition.

New Zealand is 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 an unrelated incident at a Countdown store in Dunedin that left four people injured.

-with AAP