A full investigation into what caused the fire at SkyCity's International Convention Centre in Auckland has started today.

Photo: RNZ/Amy Williams

Fire and Emergency said it was now safe enough for fire investigators, the police and construction staff to start looking at how the blaze began.

Senior station officer Frank Walsh said one crane positioned on Nelson Street is dedicated entirely to that investigation.

"They've put that up [there because it's] the best access to where they believe is the probable point of origin and that crane may stay in place for the length of the weekend," he said.

"Because it's the holiday weekend, we're making the most of the reduced traffic and we'll probably keep that on site, perhaps even until Tuesday."

Mr Walsh said they were using another three cranes to help firefighters tackle hotspots.

"They're being used to transfer personnel to the roof areas where the hotspots are occurring, that way we can address the hotspots but still be safe - fully supported within the crane basket," he said.

Up to 25 firefighters are at the scene today and six engines.

Parts of Hobson Street and Wellesley Street West directly next to the centre are still closed, but one lane is open on Nelson Street.

Concerned workers strike over safety

Meanwhile, some SkyCity workers are on strike until next Tuesday because they say they have not received formal, written clearance that the building is safe to be in.

Joe Carolan from Unite Union said workers are concerned.

"When we get sick, we have to produce [a medical certificate] from our doctors but we have received nothing in writing from SkyCity proving that place is safe," he said.

But SkyCity said independent consultant Miller Hygiene Consultancy has confirmed the air quality in its precinct is very good.

It said about 50 staff members are on strike and it has had minimal impact on operations.

SkyCity said WorkSafe had also examined the precinct and was satisfied the company had taken appropriate actions to manage any potential health related risks.

Photo: Fire and Emergency New Zealand

Offer of help for construction workers

Chief executive of the Auckland Chamber of Commerce Michael Barnett said many construction workers will not yet know when they can return to the building site.

He said this will be a frustrating time for workers in the precinct, including those in retail and hospitality.

If they are experiencing hardship or loss of income, they can contact the Chamber to be put in touch with the appropriate government agency, he said.

Auckland Regional Public Health Services has released information for businesses and residents who will need to clean up following the fire.

People are advised to ventilate any buildings impacted by the smoke and to clean air conditioning units.

Meanwhile, it's still not clear if the country's second busiest court will re-open on Tuesday next week.

The Auckland District Court was forced to close on Wednesday, over concerns about air quality.

Ministry of Justice acting chief executive Carl Crafar said contractors will be working this weekend to check if the Auckland District Court, Chorus House and Swanson House are fit to be occupied.

He said a decision will be made at the weekend as to whether or not court services will resume on Tuesday.