The bomb was found yesterday in Cologne city during construction work near a 45-storey building housing about 2,000 people.
The tricky construction of the fuse prompted bomb disposal experts to opt for a controlled detonation of the bomb and residents within a radius of 300 meters of the detonation site were evacuated, local media reported.
Earlier this month, a construction worker manning a digger was killed when he accidentally struck a World War II-era bomb during excavation work in Euskirchen in Germany's western state of North Rhine-Westphalia.
Nearly 69 years after the end of World War II, thousands of unexploded bombs are still believed buried in Germany.