It all started with people complaining of breathing difficulties after being exposed to unidentified unpleasant odors at the airport in Hamburg on Sunday morning, Hamburger Morgenpost reported.
Terminal 1 and 2 were then evacuated and hundreds of passengers had to wait outside at almost below zero temperatures.
A pepper spray or a similar substance is most likely behind the incident, a spokesman for the firefighters said, noting that a refill cartridge had been found which could have caused the health problems, DPA reported. The substance was then presumably spread through the building by the air-conditioning system.
The possibility of a terrorist attack has been ruled out, the spokesman added.
An airport official said earlier that a gas leak could be behind the breathing problems, irritated eyes, and nausea, DPA reported.
The environmental services of the fire brigade are currently trying to establish exactly what the substance was.
The firebrigade that responded to the call set up first aid posts for those who had inhaled the substance.
Flights were canceled for more than an hour because of the emergency, Hamburg airport said on Twitter.