(CNN) Residents of Ahlbach, Germany, were mostly asleep at about 4 a.m. Sunday when they were jolted by a sudden blast.

Something seemed to have exploded, large enough to feel like an earthquake, and a massive crater in a cornfield was all that remained.

Police were sent to inspect the hole, which measured 33 feet wide and 13 feet deep, they said

Was it a World War II bomb? At first, officials weren't sure. But after a day studying the crater, they said it "almost certainly" was a 550-pound dud.

"With the former railway depot, we were quite a bomb target at the end of the Second World War," city spokesman Johannes Laubach told the German news website Hessenschau . "We can be glad that the farmer was not in the field."

Read More