Massey University spokesman James Gardiner said the preliminary conclusion was that the smell was caused by material from an autoclave used in the science building to dispose of biological material being ventilated into the student centre.
An autoclave is used to sterilise equipment and supplies for disposal by subjecting them to high pressure saturated steam.
"One of the six staff members present described the smell as chemical and believed it may have been caused by formalin - formaldehyde," said Mr Gardiner.
"Others described it in various ways, including chemical, meaty, sewer-like, decaying material and rotten eggs. They reported symptoms including sore throats, headaches, nausea and itchy eyes. All of the staff from the medical centre were offered medical examinations, one of whom took this up. None have ongoing symptoms."
Mr Gardiner said immediate measures were taken to ensure the safety of the air supply.
While formaldehyde was initially suspected, Mr Gardiner said it was now considered "unlikely" that the chemical was contained in the contaminated air. But during the investigation a second incident involving formaldehyde exposure on May 17 and 18 came to light.
"It involved 12 staff, one of whom transported pig carcasses that had been embalmed in formalin and the others who were present when the container the carcasses were in was opened," Mr Gardiner said.
"It appears the carcasses, which come from an external supplier, had not been correctly cleaned after embalming."
Five of the staff sought medical treatment for symptoms including sore throats and eyes, headaches and breathing difficulties.
University management had also been made aware of at least one staff member raising concerns about ventilation standards in the science building for more than a year.
Mr Gardiner said those concerns would also be thoroughly investigated.
"To prevent any recurrence of the May 29 event, the university has stopped using volatile material in the science labs while it investigates modifying or upgrading the ventilation systems in both buildings.
"These are new buildings, opened within the past two years and fully comply with building standards. Independent testing has been carried out in both buildings in the weeks since the incident, which have all been clear.
"There have been no reports of students complaining of issues with odours or chemicals."
Massey advised WorkSafe on what has occurred and on the actions being taken to investigate the incidents and prevent any recurrence.
A WorkSafe spokesman said anonymous information was also passed on.
"WorkSafe made follow-up inquiries but decided to take no further action," he said.