Six people were mysteriously struck down with breathing problems at Frankfurt Airport on Monday morning. Firefighters were called to Terminal 1 after several people reported breathing problems at the check-in counters around 11am. The people were treated at the scene and after no trace of gas was detected the counters were reopened, according to The Local. The incident was initially reported by Bild as a gas attack, with the paper saying an unknown assailant had sprayed passengers with a mystery substance. However, it now appears that information was incorrect. Airport authorities say the exact cause of the incident is still unclear, but investigations are ongoing. The check-in area was closed for a short time after the scare, before being reopened around 12.30pm. Nobody was seriously injured during the incident.