The fire in Auckland's SkyCity convention centre is under control but toxins from the smoke are expected to persist for a long time after the fire has been put out.
Smoke is a mixture of toxic gases and particulates. What particulates are present depends entirely on what has been burnt, according to air-quality testing organisation K2 Environmental.
K2 says the fire could contain "thousands" of particulates all with separate health effects.
"If plastics have burnt in the fire then the smoke will contain organochlorine compounds, many of which are carcinogenic," it said in a blog post on Thursday.
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Burning plastic also generates dioxins and furans, both of which are highly toxic and can have long-lasting health effects.
Short term exposure can result in skin lesions and altered liver function according to the World Health Organization.
Both dioxins and furans can cause birth defects, liver damage and cancer.
The burning of the bitumen roof is expected to generate poly aromatic hydrocarbons. These can cause nausea, vomiting, and eye irritation.
Hydrogen cyanide is expected to be in the smoke too - it is generated through the burning of wool, nylon, rubber, and polyurethanes.
Exposure to hydrogen cyanide can cause headaches, drowsiness, vomiting and flushed red skin.
It can lead to irregular heart rate, reduced body temperature and, if left untreated, it can be fatal.
Multiple particulates in the smoke will also be present, each with different health implications.
Ultra-fine particulates will cause irritation to the eyes, nose and throat. They can also cause headaches, fatigue and nausea.
Black carbon particulates are very small and will progress deep into the lungs.
It can also absorb other toxic gases and carry them into the lungs. The darkness of the smoke plumes over the city indicates a high presence of black carbon.
Fine particulates are similar to ultra-fine particulates and can also carry toxins into the body.
The closer people are to the source of the fire, the higher the likelihood they will be exposed to toxins in the smoke.
K2 recommends leaving any smoke affected property immediately and staying away until all smoke has dissipated.
"This may take days as air conditioning systems can be overloaded with toxins and will require a complete service. The air conditioning systems will spread the toxins throughout the building," it said on Thursday.
"People who live in smoke affected properties are likely to be more at risk than those that work in a building for eight hours a day."
K2 recommends having the air quality of your home tested before re-entering the building.
NIWA's leading air quality researcher Dr Guy Coulson advises those living or working in the CBD to follow Auckland Regional Public Health Service's advice to keep windows closed and turn external air conditioning off to avoid bringing smoke inside. But his number one tip: "Simply don't go there."
Anyone with concerns for their health is urged to call Healthline on 0800 611 116 or seek other medical assistance.