Five people are being treated in hospital with stab wounds after a man allegedly attacked employees and shoppers inside a busy supermarket in New Zealand.

Radio NZ reported the New Zealand Prime Minister Jacinda Ardern has been briefed but said a motive for the attack was not known.

“Prime Minister Jacinda Ardern says it is not known what was the motivation behind the stabbing attack in Dunedin, but has been advised that there is nothing to indicate it is a domestic terror event,” the news outlet posted on Twitter.

NZ news outlet Stuff reported eyewitnesses heard loud screaming and “saw a man brandishing two knives” at a supermarket in Dunedin on the country’s south island in a horror attack on Monday.

“It just sounded like someone fell over and then screaming got louder and louder,” a witness told the news outlet.

The Otago Daily Times reported members of the public tackled the alleged offender to ground before armed police arrived. He was then marched, covered in blood, to the nearby police station.

Police praised the actions of bystanders. who attempted to those who tried to stop the alleged attacker.

“It is nothing short of heroic,” District Police Commander Superintendent Paul Basham said.

I think have acted selflessly and with great courage to prevent this man from hurting anybody else, and indeed I think they did just that,” he said..

He is now in custody.

Radio NZ reported the attack took place at the Countdown Dunedin Central, just metres from the iconic Dunedin Railway Station and the city’s heart, the Octagon at 2.30pm (NZST).

St John Ambulance officers confirmed three people were being treated with critical injuries and another two have been injured in the afternoon attack.

Tweet from @nzpolice

All five victims were rushed to hospital.

Countdown spokeswoman Kiri Hannafin said two of the injured were employees.

The company’s managing director Spencer Sonn said the company was “shocked and devastated” by the events and the store would remain closed for the next few days.

He said their priority was “our injured team members and caring for our wider team in the wake of this extremely traumatic event”.

“We are deeply upset that customers who tried to help our team members were also injured,” Mr Sonn said.

Witnesses told Stuff the attacker was “quite a messy little fellow” with curly hair.

-with AAP