A teenager - possibly an apprentice - is believed to have accidentally left unattended the blowtorch that sparked the devastating SkyCity fire, bringing central Auckland to a standstill.
A well-placed source told the Herald the teenager, who was working for a sub-contractor, was called for a smoko break and only remembered when he was away from the roof that he may have forgotten to turn off the gas blowtorch being used to help install waterproof membrane.
The source understood he was returning to the roof to check the blowtorch but by then the fire had started.
"The poor guy is in tatters ... he's completely shattered."
It is understood part of the investigation will look at supervision and experience of the workers on the roof.
SkyCity Entertainment Group's chief executive Graeme Stephens said there were surveillance cameras operating in the precinct but he didn't know how the fire started.
He was however concerned about the worker who is alleged to have been involved.
"We have been worried about that person. We don't know who it is. There's certainly no witch hunt from our side. We have a genuine concern for their mental health and wellbeing.
"We're not trying to find them and get them back. We don't know the cause of the fire. We have concern for anyone involved. We're absolutely of that view. We need to get to the cause, obviously."
Asked if any video footage was available that identified how the fire started, he said: "We have got our normal surveillance cameras in place."
It is unclear where the teenager is now or if he has been officially spoken to about the events of last Tuesday.
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A worker on the site told the Herald there were two young workers on the roof that day.
Despite being young and often working on their own they seemed to have a fair bit of experience, he said.
"From what we and what I saw...they were skilled guys. I wouldn't say that because they look young that they were necessarily apprentices. They might have been some of the more skilled guys on the team.
"I know when they lay the roofing, they actually - the way they worked and the way that they did the roof - they looked like they were very skilled and that they'd [been] doing it for quite some time."
The worker said there were up to 15 CCTV cameras around the building but the ones on level five and six were not pointed at the roof entry.
MPM Waterproofing Services general manager Andrew Pardington told the Herald that afternoon he had a team of up to 12 waterproofers at the convention centre when the blaze broke out.
He had a debriefing with them afterwards but would not say what was discussed in regards to how the fire started.
When asked specifically if a worker left a blowtorch on while having a break he said: "From my understanding that's not what happened but there was a whole lot of conversation heard on site, but really it should be left to the investigating team to find out what happened."
According to a Herald source it was only once investigators went through surveillance camera footage that they discovered what happened.
This morning Pardington refused to confirm or deny the allegation about how the fire started.
He said he was unable to comment on the actions of his staff or the origin of the fire due to the ongoing investigations.
"I really don't have anything to add at the moment, unfortunately," he said.
Pardington said at the time that Health and Safety had been discussed and support offered to his staff during the debrief immediately after the fire. He said they all appeared to be ok.
"None of my staff were injured which I was really happy about."
A WorkSafe spokeswoman said it was unlikely the agency would be able to comment on any specifics, saying it has only been notified and making initial inquiries.
No one was immediately available to comment from Fletcher Building.
More than 150 firefighters were involved in battling the blaze which saw thick black toxic smoke pour from the rooftop for four days.
Guests were moved from SkyCity's hotel The Grand and put up in other accommodation. The casino, restaurants, carpark and Sky Tower were all closed that afternoon, as were other nearby buildings, including the District Court, in following days.
Several streets around the convention centre remained closed until today, causing massive traffic disruptions in the city.
Fletcher Building and SkyCity Entertainment confirmed they have contract works and third party liability insurance in place on the New Zealand International Convention Centre construction site.
A construction expert said it was too early to tell if any party will become liable, as it would depend on the reason for the fire.
Fire and Emergency NZ region manager Ron Devlin said today two fire trucks remained at the scene. The last flare up was 6pm last night.
"Representatives from 10 different organisations including police, insurers and other government agencies have been conducting a cooperative investigation.
"The weather has been favourable to us over the weekend, allowing our teams to examine the roof area in baskets suspended by cranes."
Significant damage to the roof was hampering efforts to access it.