Mystery still remains over what the substance was that caused 16 Qantas office workers to fall ill after breathing in a noxious odour in a 16-storey building last week.

A Qantas spokesperson said the airline was continuing to work together with the property manager Bayleys and WorkSafe NZ to understand what caused the incident and to make sure it did not happen again.

Various tests carried out after the incident throughout the weekend did not pick up any further issues or abnormalities and will continue over the next two weeks. Air monitoring systems were also put in place.

Bayleys commercial property manager Hamish Mackereth said the cause is still being investigated.

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"Further minor testing will continue for the next two weeks to exhaust all possible causes of the suspected contaminated leak."

A WorkSafe spokesperson confirmed it was leading the investigation into the incident but it was likely to take some time before any conclusions are reached. WorkSafe would not provide progress reports on the investigation citing legal reasons.

Of the 100 Qantas staff in the building at the time, 16 were treated at hospital after being exposed to the smell which caused nausea, headaches and vomiting. They were all discharged by Thursday night.

An Auckland DHB spokeswoman said the emergency department cared for those patients with mild to moderate symptoms in its emergency department. All the patients were observed for four to eight hours before being discharged home.

Fire and Emergency completed its work on the building on Friday and left it with WorkSafe investigating and the Auckland Regional Public Health Service interviewing people to determine the time of the exposure and the symptoms they experienced.

Dr Denise Barnfather, ARPHS Medical Officer of Health, said last week that the people exposed to the chemical and were experiencing symptoms such as headaches, dizziness, nausea, vomiting, blurred vision, shortness of breath or chest tightness should seek medical attention immediately.