Ten different organisations are investigating the blaze that ripped through the roof of a $700 million building in central Auckland.

The latest flare-up at the New Zealand International Convention Centre at Sky City occurred about 6pm yesterday, but firefighters have been able to scale back their presence at the site.

"There are now two trucks present at the site," Fire and Emergency New Zealand region manager Ron Devlin said today.

More than 150 firefighters were involved in battling the blaze, which saw toxic thick black smoke pour from the rooftop for four days.

"The weather has been favourable to us over the weekend, allowing our teams to examine the roof area in baskets suspended by cranes," Devlin said.

"The significant damage to the roof has been hampering efforts to access it."

Devlin said the investigation, which included mapping affected areas, was ongoing and it was not yet known how long it would take.

Representatives from 10 different organisations including police, insurers and other Government agencies have been conducting a co-operative investigation, he said.

Fletcher Construction has been assisting in providing resources, including large cranes for accessing and examining the scene, he said.

SkyCity Entertainment Group's chief executive Graeme Stephens earlier told the Herald there were surveillance cameras operating in the precinct but he did not 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," Stephens said.

"There's certainly no witchhunt from our side. We have a genuine concern for their mental health and wellbeing."