The explosion left a 10-metre wide and four-metre deep hole after residents in Limburg, in Hesse, heard a loud noise and felt the earth shake at 3:52 am on Sunday morning. No one was injured.
“The crater was examined on Monday by an explosive ordnance clearance service to find possible fragments,” a police spokesman told AFP.
“The area was used for target practice during the Second World War,” he added.
A bomb disposal service spokesman said it was “highly possible” that a WWII ordnance was involved.
A local government spokesman in the nearby city of Darmstadt told German daily Bild it was believed the bomb had a chemical-based delayed timer which could have finally eroded.
“We are lucky that the bomb exploded in a field,” he said. “Many bombs were dropped over cities and airports.”
Nearly 75 years after the end of war, Germany remains littered with unexploded ordnance, a legacy of the Allied bombing campaign against Nazi Germany.
However, most of the bombs found are detonated before they can cause an explosion.
Earlier this month, a 100-kilo US bomb from the war, discovered during building work near a shopping complex, was defused in central Berlin after the evacuation of around 3,000 people.
According to experts, 10 percent of the millions of bombs dropped on Germany during the conflict did not explode.