The authorities are now trying to find the source of the fumes which forced the closure of the Central Sorting Office of the Post and Telecoms Department in Kingston earlier today.
The fumes forced more than 600 people to evacuate the building.
The police say about 60 persons, including students, experienced respiratory problems and had to be taken to hospital for medical attention.
Earlier, a staff member at the department told our news centre that the substance was especially potent on the first floor.
She said several persons became ill and it was decided that everyone should leave the building.
Meanwhile, Director General of the Office of Disaster Preparedness and Emergency Management, Ronald Jackson, said his agency, the National Environment and Planning Agency and the Fire Brigade are investigating the matter.
Jackson said they are seeking to determine the source and the nature of the fumes.
He says NEPA has collected readings from the atmosphere in the area.
Jackson said initial checks show that the fumes may not have originated from the Central Sorting Office building.
He says the agency has asked that activities in the area be curtailed to facilitate the investigation.
Jackson also noted that it's expected that normal activities will resume in the area tomorrow.
The police had ealier cordoned off North Street and South Camp Road but they have since been reopened to vehicular traffic.
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