German police put parts of Terminal 1 at the major city airport on lockdown due to an emergency.
A police spokesman said an unauthorised man had got past the security area and disappeared, according to German newspaper Bild.
He was reported to have a child with him.
Federal police posted on Twitter: «In area A of Terminal 1 at the #Frankfurt #airport, there are police intervention measures.
«This includes an immediate boarding stop and clearing the security area in levels 2 and 3. Further information will follow.
«Observe the instructions of the security personnel and contact the airport operator if you have any questions.»
The man is now unauthorised inside Terminal 1.
Police chiefs later tweeted: «The reason for the police measures is the indication of the unauthorised access of at least one person to the security area. #Terminalräumung #BPol»
Investigations are underway to establish how the man managed to evade security.
But he is said to have entered the security area of the terminal with a child when the security guards were briefly distracted, according to German newspaper Frankfurter Allgemeine Zeitung (FAZ).
In area A of Terminal 1 at the #Frankfurt #airport, there are police intervention measures
Reza Ahmari, spokesman for the Federal Police said «at least one person» had reached the area behind the security controls unchecked at about 11.15am (local time).
The security areas in levels 2 and 3 of the airport have been evacuated.
Unverified footage on social media shows the mass evacuations of hundreds of passengers by armed police.
One passenger tweeted: «There was some sort of security breach here at the Frankfurt Airport.
«We just went through a mass evacuation orchestrated by armed officers and airport security. No flights are boarding or leaving. No one knows what’s going on. They’re just telling everyone to go outside.»
Boarding at the airport was stopped at about 11.30 am, a spokeswoman for the airport operator Fraport said.
A spokeswoman told FOCUS Online that areas A and Z in Terminal 1 were affected.
She advised passengers to leave Frankfurt Airport today and contact their airline for possible cancellations or delays.
Frankfurt airport tweeted: «Due to a police action, the German Federal Police is currently evacuating Piers A and Z at Frankfurt Airport’s T1.
«As a result of this measure, flight disruptions can be expected. Passengers are advised to check the status of their flight.»
A total of 1,500 arrivals and departures are planned in Frankfurt today.
By 1pm 39 of them had already been cancelled.
German airliner Lufthansa has stopped large parts of its check-ins because of the evacuation.
In areas A and Z, passengers can not get on or off the planes, the company said.
Arriving aircrafts had to wait on the apron with passengers on board.
It comes after authorities at Munich Airport closed Terminal 2 after a person managed to skip security checks, which resulted in 200 flight cancellations.
Additional reporting by Monika Pallenberg