Some 600 people have been evacuated from their homes in the old city of Frankfurt so specialists could remove a World War II-era bomb that was discovered in the Main River.

The German news agency dpa reported the bomb was defused, as planned, underwater on Sunday, which led to a loud detonation and a big water fountain on the river. Police told dpa "the bomb is no longer a danger".

Firefighters had discovered the American 250kg during diving training in the river on Tuesday.

Even more than 70 years after the end of the war, bombs and other munitions still turn up regularly in Germany, a testament to the ferocity of the fighting in World War II.