Eleven people were cared for by ambulance staff after experiencing dizziness and facial numbness, said police.
The affected premises in Solna municipality in Stockholm county house both the Karolinska Institute and the Royal Institute of Technology as well as several privately-owned companies, wrote Aftonbladet.
The Swedish tabloid reported that the leak was believed to have started on the seventh floor of the building in a laboratory area used by a biochemical company which also is located in the building.
“There has been a discharge of gas in this room. It is probably the chemical toluene. In concentrated form it constitutes a fire and explosion hazard,” police spokesperson Sven-Erik Olsson told the newspaper.
Police and emergency services examined the building, which was cordoned off between 1pm and 3pm.
One of the individuals affected by the incident was Sci Life Lab safety officer, Erik Malm.
“It's OK now, it was something chemical,” he told news agency TT. “There was a strong chemical smell on a couple of floors, but we haven't been able to locate a source,” he added.
Police later said that there was no longer any risk of explosion and no suspicion of any criminal activity.
“An unknown person had spilled or thrown the substance in a bin. A cleaner had then brought the substance into the room,” confirmed police spokesperson Albin Näverberg to TT.