Disturbing details have emerged about the man who killed two co-workers and injured at least six others in a shooting spree at a New Zealand building site.

Aucklanders on their morning commutes were shocked early on Thursday, hearing gunfire outside a building on Queen Street, the city’s main thoroughfare, about 7.20am (local time).

Dozens of police vehicles, a helicopter and several ambulances scrambled to attend once the threat became clear.

The gunman has been identified as 24-year-old Matu Tangi Matua Reid. He worked in the building, and arrived on Thursday morning with a pump-action shotgun.

Reid’s co-workers thought it was a joke – until he opened fire.

Witnesses have told New Zealand media of seeing the gunman walk calmly through the nearby Britomart rail station moments before he stormed the One Queen Street building.

Construction workers said he came up the stairs, yelling at them to get on the roof or he would shoot.

“We went to 12, and other guys said go up, so then we went to 16 and stopped because no one knew [what was going on],” one worker told the NZ Herald.

He heard gunshots, and saw a man fall to the concrete floor.

Other workers began leaving the building when the fire alarm went off. Only when people started running and shouting did they realise it was an emergency.

Reid was sentenced to five months’ home detention in March on charges of injuring with intent to injure, wilful damage, male assaults female and impeding breathing.

New Zealand laws allow people sentenced to home detention to continue to work.

Police said Reid “moved through the building site [on Thursday] and continued to discharge his firearm”.

“Upon reaching the upper levels of the building, the male has contained himself within the elevator shaft,” they said on Twitter.

“Further shots were fired from the male and he was located deceased a short time later.”

The shooter has been named as Matu Tangi Matua Reid, who was serving a sentence for domestic violence offences. Photo: Supplied

Local television outlets broadcast footage of workers on the roof of the building taking shelter behind packs of pre-mix cement.

Police Commissioner Andy Coster said they had “contained the situation and were not seeking anybody else”.

“Thankfully, many people were able to escape the building. But I know that for those who hid or remained trapped, this was a terrifying experience,” he said.

The shooting is being treated as an isolated incident, not a national security threat, with no change to the country’s terror settings.

New Zealand Prime Minister Chris Hipkins said it had been a “grim morning”. He said he had “deep sorrow” for the two victims, who were civilians killed inside the building.

“I want to thank the brave men and women of the New Zealand police who ran into the gunfire, straight into harm’s way in order to save the lives of others,” he said.

“These kind of situations move fast and the actions of those who risked their lives are nothing short of heroic.”

Streets were blocked off around the One Queen Street building into the afternoon. Photo: Getty

Shooter ‘had no history of violence’

Mr Coster said Reid had indications of a “mental health history”, and they believed his motivation was linked to his employment.

Mr Coster said it was unclear whether the attack could have been foreseen by police, or prevented. He said Reid was known for his family violence history, but had no history of showing other risks.

“Any time [sentencing] decisions are being taken, there is a weighing of risk,” he said.

“There was nothing to suggest that he has presented a higher level risk than was indicated.”

Police have confirmed Reid had no gun licence.

“There has been previous search of his property, but never found him in possession of a firearm,” Mr Coster said.

St John Ambulance general manager of operations Stuart Cockburn said 10 patients had been assessed, and seven taken to hospital.

They included the injured police officer, who was to have surgery on Thursday afternoon.

A woman at an Auckland property linked to Reid told NZ news outlet Stuff that she spoke to him late on Wednesday.

“He said he loved us and nothing really,” she said.

”His phone went dead this morning. He was talking to us last night. Everything was all good last night.”

Australian Prime Minister Anthony Albanese, who is to visit Wellington next week, offered condolences.

“I’ve been in contact with with Chris [Hipkins] this morning … it is very sad indeed to see another dreadful shooting with fatalities,” he said.

The incident occurred on the first day of the Women’s World Cup, with NZ to play Norway in the tournament’s opening match at Eden Park later on Thursday.

Mr Hipkins said there would be no change to the tournament schedule, following conversations with FIFA officials.

The Norwegian team is staying at a hotel near where Thursday morning’s shooting occurred.

Mayor Wayne Brown told TVNZ the attack was “dreadful”.

“It couldn’t have come come at a worse time given the world has its eyes on us now with the FIFA soccer thing,” he said.

-with AAP