According to German Focus Online publication, German federal police are looking for a man who managed to pass through a door at Cologne Bonn Airport in the security area in Terminal 1 at around 11am local time.
As a result all flights at Cologne-Bonn Airport have been stopped.
All aircraft have returned to the terminals as a safety precaution.
The terminal has been completely cleared and all people are being required to pass through security again. The security alarm has not affected aircraft looking to land at the terminal.
A search is taking place at present to try and find the trespasser. It is unclear at which part of the airport the person has breached security.
Police is still assuming a passenger who used the exit door into the terminal instead of passing through security and enter the secured area may have done so without criminal intention and may have not even aware of him causing this situation.
Out of precaution explosive sniffing dogs were brought to the airport and a crisis committee in Cologne is discussing the situation at this time.
This latest incident will come as further embarrassment to the airport, after the transportation hub accidently published plans on the internet in April of how it would combat a possible terrorist emergency.
The 230-page document gave a comprehensive plan for how to react in case of a whole range of emergencies, from natural disasters to kidnappings or terrorist attacks. The phone numbers and contact details of key security personnel were also published online.
However, unbeknown to the authorities, their best-laid plans were available for any potential terrorists to see on the internet. The documents would also provide them with invaluable information such as potential escape routes.
The mishap came months after a report by the German television station WDR, which revealed that Cologne-Bonn Airport’s security system failed to detect dangerous items in carry-on luggage.
EU inspectors carried out tests at the airport in February and tried to smuggle weapons and bomb-making equipment through security. Alarmingly, these objects were only detected six out of 12 times by the security staff manning the x-ray machines.
When the staff were given an advanced warning that dangerous items could be carried through security, the detection rate actually worsened, with nine out of 12 dangerous items managing to get through unnoticed.