WELLINGTON, New Zealand >> New Zealand authorities were so worried about an Islamic extremist they were following him around-the-clock and were able to shoot and kill him within 60 seconds of him unleashing a frenzied knife attack that wounded six people Friday at an Auckland supermarket.

Three of those stabbed were seriously injured.

Prime Minister Jacinda Ardern said the incident was a terror attack. She said the man was a Sri Lankan national who was inspired by the Islamic State group and was well known to the nation’s security agencies.

Ardern said she had been personally briefed on the man in the past but there had been no legal reason for him to be detained.

“Had he done something that would have allowed us to put him into prison, he would have been in prison,” Ardern said.

The attack unfolded at about 2:40 p.m. at a Countdown supermarket in New Zealand’s largest city.

Police Commissioner Andrew Coster said a police surveillance team and a special tactics group had followed the man from his home to the supermarket.

But while they had grave ongoing concerns about the man, they had no particular reason to think he was planning an attack on Friday, Coster said. The man appeared to be going into the store to do his grocery shopping as he had in the past.

“He entered the store, as he had done before. He obtained a knife from within the store,” Coster said. “Surveillance teams were as close as they possibly could be to monitor his activity.”

Coster said that when the commotion started, two police from the special tactics group rushed over. He said the man approached police with the knife and so they shot and killed him.

One bystander video taken from inside the supermarket records the sound of 10 shots being fired in rapid succession.

Coster said there would be questions about whether police could have reacted even quicker. He said that the man was very aware of the constant surveillance and they needed to be some distance from him for it to be effective.

Ardern said the attack was violent and senseless, and she was sorry it had happened.

“What happened today was despicable. It was hateful. It was wrong,” Ardern said. “It was carried out by an individual. Not a faith, not a culture, not an ethnicity. But an individual person who is gripped by ideology that is not supported here by anyone or any community.”

Ardern said the man had first moved to New Zealand in 2011 and had been monitored by security agencies since 2016. She said authorities are confident he acted alone in the attack.

Ardern said legal constraints prevented her from discussing everything that she wanted to about the case, but she was hoping to have those constraints lifted soon.

Some shoppers in the supermarket tried to help those who had been wounded by grabbing towels and diapers and whatever else they could find from the shelves.

“To everyone who was there and who witnessed such a horrific event, I can’t imagine how they will be feeling in the aftermath,” Ardern said. “But thank you for coming to the aid of those who needed you when they needed you.”

Extremist ideology is rare in New Zealand and Ardern said that only a tiny number of people would be subject to such intense surveillance.

Auckland is currently in a strict lockdown as it battles an outbreak of the coronavirus. Most businesses are shut and people are generally allowed to leave their homes only to buy groceries, for medical needs or to exercise.