Germany's busiest airport was shut down for nearly two hours on Monday after a drone was spotted near the facility, federal police said.
A pilot reported the drone over the southern part of Frankfurt's international airport at around 11.15am - the airport was subsequently shut while police searched the area with the support of a helicopter.
Police tweeted that the airport was reopened at 1pm but the investigation was continuing.
Several flights were cancelled or re-routed.
One passengers documented his journey on Twitter after his flight was diverted to Nuremberg from where he says passengers were driven to Frankfurt.
The governor of the western German state of North Rhine-Westphalia, Armin Laschet was on board one of the affected flights - he had been returning from a visit to Israel. .
Only a few weeks ago, Frankfurt airport had to be shut down for about an hour because of a drone sighting and in 2019, some 28 drone sightings were reported there, the dpa news agency reported.
Reports of drone sightings caused chaos at the UK's Gatwick airport in December 2018. Some 120,000 passengers who were due to fly were left unable to travel, while many inbound flights were diverted.