The SkyCity inferno that has sent a haze of smoke over the city and closed major roads has been brought under control but its effects are expected to be felt well into the future.

At its peak, 150 firefighters along with 30 fire appliances tackled the blaze in the $700 million New Zealand International Convention Centre, which is still under construction.

Late yesterday afternoon Fire and Emergency New Zealand (Fenz) announced the blaze, contained to the convention centre's sixth and seventh floors, had been brought under control.

"We are without any doubt winning the battle against the fire," Fire and Emergency regional manager Ron Devlin said.

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At its peak 150 firefighters have been battling the SkyCity inferno. Photo / Jason Oxenham
At its peak 150 firefighters have been battling the SkyCity inferno. Photo / Jason Oxenham

That it was such a large unfinished construction site made it one of the most challenging fires tackled in recent memory, but their approach of letting the roof burn out was proving successful, he said. It was expected to have fully burned through by 8pm on Wednesday.

Still, motorists were advised to avoid the central city on Thursday, including parts of Hobson St, Nelson St and Wellesley St. Those who could work from home or non-central locations were advised to do so.

Auckland Regional Public Health Service was also continuing to advise people to take precautions due to lingering smoke affecting air quality across the CBD.

Focus Live: Firefighters are 'winning the battle' against the fire

One firefighter was taken to hospital on Wednesday with moderate injuries, after being struck by a piece of falling roof and suffering a concussion.

"It was unusual, and may have been flicked off in the wind," Devlin said.

"It is not what we want to happen, and the reason we have been very careful with internal operations."

St John confirmed to the Herald another five people were treated at the scene for minor injuries.

Focus: Firefighters continue to battle the blaze at SkyCity Auckland. Video / Grant Murray / Supplied

While the fire had affected the sixth and seventh floors, Devlin said the fifth floor looked in good shape. The roof's membrane was damaged, but structure looked to be intact.

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"We expected the roof to burn and collapse in, and it is doing exactly that."

Once the roof had burned through they would be able to enter the building and tackle the fire internally.

Prime Minister Jacinda Ardern said she wanted to acknowledge the firefighters who had been working under difficult circumstances.

"The team on the ground have been incredibly professional, very focused on what they can do to preserve the building."

Prime Minister jacinda Ardern takes a tour of the burning convention centre with Mayor Phil Goff and Fire and Emergency's Ron Devlin. Photo / Dean Purcell
Prime Minister jacinda Ardern takes a tour of the burning convention centre with Mayor Phil Goff and Fire and Emergency's Ron Devlin. Photo / Dean Purcell

Apec 2021 would still be held in Auckland, but where it would be held was a point of discussion for Government.

"New Zealand has hosted Apec before ... without a convention centre. We had contingency in place."

SkyCity chief executive Graeme Stephens said he hoped staff working on the project would be back at work on Friday.

Auckland Transport said parts of Hobson St, Nelson St and Wellesley St remained closed, and that motorists should avoid the area or expect delays.

Fire fighters attempt to extinguish the fire at the New Zealand International Convention Centre. Photo / Jason Oxenham
Fire fighters attempt to extinguish the fire at the New Zealand International Convention Centre. Photo / Jason Oxenham

"If you are able to time your travel to avoid peak hour traffic, by leaving earlier or later than usual, we advise you to do so," AT spokesperson John Nottage said.

People were also encouraged to avoid unnecessary travel into the central city on Thursday, and work from home or a non-central location if possible.

Train services were not affected by traffic diversions, however some bus routes had been altered.

Auckland Regional Public Health Service advised people living or working near the convention centre to take precautionary measures to avoid breathing in the smoke, along with their pets.

People who smoked, the elderly, children, and those with heart disease, asthma or other lung conditions were at greatest risk of harm from smoke inhalation and should avoid exposure.

Fenz was also working hard to ensure any run-off from water used to fight the fire was minimised, and Auckland Council and Watercare were monitoring this as the incident continued.

While officials refused to speculate on how the fire started, construction workers said they believed an unattended blowtorch could have ignited the straw-like acoustic layer, quickly spreading to the roof's bitumen membrane.

For two days central Auckland has been enveloped in thick black smoke disrupting many businesses and leaving workers feeling nauseous, meanwhile several busy central roads have been closed.