Rescuers evacuated people from all airport terminals.
According to preliminary data, toxin was believed to be spreading through the airport's air conditioning system.
More than 50 people were affected as a result of the incident. They were complaining about breathing problems and burning eyes.
Specialists have not figured out the origin of the substance yet.
“We’re working closely together with the authorities to find out more," an airport spokeswoman, Karen Stein, said.
Halted flights were resumed at 1:30 p.m. local time, access to the airport terminals was opened.