New Zealand Prime Minister Jacinda Ardern said on Friday a stabbing incident at a supermarket in Auckland that left six people injured was a "terrorist attack" carried out by a "violent extremist."

"What happened today was despicable, it was hateful, it was wrong," she said, describing the attacker as a Sri Lankan national who arrived in New Zealand in 2011.

The man, who had been a "person of interest" for about five years, was killed within 60 seconds of beginning the attack, she said, adding that he had been inspired by ISIS.

New Zealand Police Commissioner Andrew Coster also confirmed at the press conference that the individual behind the attack was under heavy surveillance over "concerns about his ideology."

The offender was acting alone and there was no further threat to the public, said Coster.

The person traveled from where he lived in Glen Eden to Countdown at LynnMall in Western Auckland, and was closely watched by surveillance teams.

He entered Countdown supermarket where he obtained a knife. Surveillance teams were as close as they could be, and when the commotion began they acted, according to Coster.

When the man approached them with the knife he was shot and killed, said Coster.

Armed police blocked off the roads nearby, and at least 10 police vehicles took up positions around the mall where the supermarket is located.

A video posted on social media showed shoppers in the supermarket shortly after the attacker struck. 

"There's someone here with a knife ...  he's got a knife," a woman can be heard saying. "Somebody got stabbed." A guard asked people to leave the shopping mall shortly before about six shots rang out.

Of the six wounded people, three were in critical condition, one in serious condition and another in moderate condition, the St John Ambulance service said in a statement to Reuters.

Witnesses told reporters outside the mall they had seen several people lying on the floor with stab wounds. Others said they heard gunshots as they ran out of the supermarket.

Videos posted online earlier showed panicked shoppers running out of the mall and looking for cover.

New Zealand has been on alert for attacks since a white supremacist gunman killed 51 people at two mosques in the city of Christchurch on March 15, 2019.

In May, four people were stabbed in a supermarket in Dunedin on New Zealand's South Island.

Read more: 

Christchurch shootings: Terrorism in the age of social media

A year after Christchurch's horrors, New Zealand has come a long way

(With input from Reuters, Xinhua)