Five workers have been taken to hospital complaining of nausea and headaches after cleaning an office and factory facility in Melbourne's south east.
Paramedics and fire crews were called to the premises on Wellington Road, Mulgrave, shortly after 2.10pm.
A spokesman for the Metropolitan Fire Brigade said fire crews were working to establish the exact cause of the incident, but it appeared the workers had been overcome by a chemical used to clean floors or carpets.
The spokesman said poor ventilation may have been a contributing factor.
An ambulance spokesman said five people had been taken to hospital complaining of nausea and headaches. He said all were in a stable condition in either Monash Medical Centre in Clayton, or Dandenong Hospital.
He said paramedics were still assessing a number of people at the site.