Frankfurt - Experts failed to defuse a World War 2 bomb found during construction work near the Frankfurt Airport and were forced to dismantle it in a controlled explosion early on Wednesday morning.

The blast created a huge crater in the heavily travelled section of autobahn near Germany's busiest airport, causing closure of parts of the highway and creating traffic jams 20km long.

The 25-metre-wide crater was up to three metres deep, a spokesman for the Offenbach police said. There were no injuries.

After discovery of the 500kg British bomb on Tuesday, landings at the Frankfurt airport were restricted. One of the airport's four runways was closed for landings because bomb disposal experts said the site where the bomb was found could not be overflown.

Planes were allowed to take off from the runway, but only in the direction away from the bomb site. By late evening, the restrictions had been lifted.

Some flights were rerouted to other airports.

Police erected a one-kilometre-wide safety zone around the bomb and evacuated 160 people from their homes. During the explosion, a safety zone of 300m was kept for the sappers.

The bomb was outfitted with a chemical detonator, increasing the difficulty of the bomb disposal team's job.

Unexploded bombs dating back to the aerial bombing of Germany during World War 2 are still frequently found. Most local authorities have teams working full-time to detect and defuse them. - Sapa-dpa