New Zealand police on Friday shot and killed a knife-wielding “extremist” who was known to authorities, Prime Minister Jacinda Ardern said, after he stabbed and wounded at least six people in a supermarket.

The attacker, a Sri Lankan national who had been in New Zealand for 10 years, was inspired by the Islamic State militant group and was being monitored constantly, Ardern said. “A violent extremist undertook a terrorist attack on innocent New Zealanders,” Ardern told a briefing.

“He obviously was a supporter of ISIS ideology,” she said, referring to Islamic State.

The attacker, who was not identified, had been a “person of interest” for about five years, Ardern said, adding that he had been killed within 60 seconds of beginning his attack in the city of Auckland.

Police following the man thought he had gone into the New Lynn supermarket to do some shopping but picked up a knife from a display and started “running around like a lunatic” stabbing people, shopper Michelle Miller told the Stuff online news outlet.

A witness told the New Zealand Herald the attacker had shouted “Allah-u-akbar” (God is greatest).

Police commissioner Andrew Coster told the briefing the man was acting alone and police were confident there was no further threat to the public.

”We were doing absolutely everything possible to monitor him and indeed the fact that we were able to intervene so quickly, in roughly 60 seconds, shows just how closely we were watching him,” Coster said.

Ardern said the reasons the attacker was known to authorities were subject to court suppression orders over legal proceedings.