Prime Minister Jacinda Ardern says the attack at the New Lynn Countdown supermarket today was a terrorist attack carried out by a violent extremist.

The prime minister and the police commissioner addressed the media after the man was fatally shot at a west Auckland mall this afternoon.

It is understood six people have been injured in the incident at LynnMall in New Lynn.

St John said three patients in a critical condition and one patient in a serious condition have been taken to Auckland City Hospital; one patient in a moderate condition has been taken to Waitakere hospital; and one patient in a moderate condition has been taken to Middlemore Hospital.

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Ardern revealed the terrorist is a Sri Lankan national who arrived in New Zealand in October 2011 and he became a person of national security interest from 2016.

The reasons he is known to agencies is subject to suppression orders, but Ardern said it was her view that it was in the public interest to share as much information as possible.

The prime minister did say the terrorist held a violent ideology inspired by the Islamic State, but it would be wrong to direct any frustration at anyone other than this individual. She said she was personally aware of the terrorist before today's attack.

Ardern said it was a senseless attack and she was sorry it happened.

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"What happened today was despicable. It was carried out by an individual."

Ardern said the individual was under constant monitoring, and he was shot and killed with in 60 seconds of the attack starting.

The police team who was monitoring shot and killed him.

Coster said the man was under heavy surveillance because of concerns about his ideology.

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He entered the store and obtained a knife from within the store before starting the attack.

Coster said surveillance teams were as close as they possible could be and when the man approached police with the knife he was shot and killed.

"I acknowledge that this situation raises questions about whether police could have done more, whether police could have intervened more quickly. I'm satisfied based on the information available to me that the staff involved did not only what we expect they would do in this situation, but did it with great courage.

"The reality is, that when you are surveilling someone on a 24/7 basis, it is not possible to be immediately next to them at all times. The staff intervened as quickly as they could and they prevented further injury in what was a terrifying situation," Coster said.

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Ardern said all legal and surveillance power has been used to try to keep people safe from this individual.

"What I can say is that we have utilized every legal and surveillance power available to us to try and keep people safe from this individual. Many agencies and people were involved and all were motivated by the same thing - trying to keep people safe."

Coster said there had been nothing that would tell police the extent of his intentions, or that he intended to do this today.

He said the individual was very surveillance-conscious, and surveillance teams needed to maintain a distance to be effective.

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An eyewitness has told RNZ she saw a man running around armed with a knife and heard many people screaming.

Another shopper who was in the supermarket at the time heard someone scream before shoppers started running towards the door.

Heavily armed police and ambulances remain at the scene.

It is the second major episode of violence at a Countdown supermarket this year.

Four people were taken to hospital after an attack at a supermarket in Dunedin on 10 May. Among those injured were two Countdown staff.

A 42-year-old man has pleaded not guilty to four charges of attempted murder.

Reporting by RNZ

Republished by Arrangement