They had no warning it was coming. But when they saw the tornado, the workmen ran for their lives.
They were putting up giant concrete pre-cast panels at the Hobsonville High School site when the wind and rain began. As it intensified, the workers looked desperately for an escape route.
One man, named by co-workers as Brendan, saw the tornado and ran towards a truck where he thought he would be safe.
A colleague said he managed to get to the side of the truck when one of the concrete panels came crashing down. The impact flattened the truck. Another man understood to have been crouching beside the driver's door was also killed.
A third person in the area also died.
A witness to the building site tragedy said ''it was just panic everywhere''.
A concrete panel that had been hanging off a crane crashed to the ground and a worker who was harnessed to the frame of the building was left dangling from a gantry. The workers were from Hawkins Construction and subcontractor Vuksich and Borich Civil Engineering.
Debris was flying in every direction and the on-site office was in ruins.
The foreman had to crawl free to escape.
A workman at the scene told of the desperate search for Brendan, a labourer aged in his 20s. He said they looked for him in his car, parked close to the spot where he died, and called out to him.
They feared he had been blown from the site on to a reserve that was littered with debris from houses.
The reality, though, was far worse.
The news was devastating.
''It's pretty hard when you have to tell [the boss] that we've lost one of the boys.''
Other workers said they had no other choice but to cling to a large truck and ''hold on for dear life''.
''I've never seen anything like it,'' one said.
The worker said the concrete panels must weigh 20 tonnes but they were being picked up ''like they were small rocks''.
As they watched the body recovery, the workers spoke of receiving no warning bad weather was on its way, even though weather alerts had been issued to the media for more than an hour.
The recovery of the bodies was hampered by heavy rain and the threat of another tornado. Concrete cutters were used to try to break up the panel and a crane was brought to the scene to try to lift it.
Hawkins Construction executive general manager Dan Ashby said the company's immediate focus was on supporting the affected workers' families, and its staff and subcontractors on site.
A staff member at Vuksich and Borich Civil Engineering said a member of staff was one of those thought to have died.
- Andrew Koubaridis