A bomb dating back to World War II was found on the grounds of Frankfurt Airport on Friday.
Police say it is a phosphorus bomb that was discovered during construction work.
Incendiary bombs containing white phosphorus were used on a large scale during World War II.
The bomb was to be detonated in a controlled manner in the late afternoon or evening.
A radius of around 1,000 metres around the site was cordoned off in advance.
Neither air traffic nor the roads around the airport have been affected so far, a spokesman said. There have been no evacuations.