The southern runway of the airport, which serves as a major hub for logistics group DHL, remained closed while specialists examined the object using explosives-disposal technology, a police spokesperson said.

Authorities were also investigating reports of an unidentified flying object potentially linked to the incident.

Several aircraft, including a passenger flight, were diverted overnight, but operations were back to normal in the morning, the spokesperson said.

German airports are on high alert after a series of unauthorized drone overflights at sites including military facilities, energy terminals, seaports and logistics companies.

Germanyâs federal police have warned that the overflights could have been organised by Russian agents.

Russia has denied any involvement in the incidents.

(Reporting by Friederike Heine, editing by Thomas Seythal)