Bomb disposal experts have safely defused two powerful World War II bombs lying on the bottom of the Rhine River in Germany.

A third device was detonated under a controlled explosion, after 45,000 people in the city of Koblenz had been evacuated as a precaution on Sunday.

It was one of Germany's biggest bomb-related evacuations since the war ended, and some 2,500 police officers, firefighters and paramedics were on duty across the city to secure the operation.

Authorities set up shelters in parts of Koblenz farther away from the bomb site, and shuttle buses were on hand in the morning to carry residents to safety.

The British bomb could have caused massive damage if it exploded. It was found last week longside a 275-pound US bomb and a smoke grenade after the Rhine's water level fell significantly due to a prolonged lack of rain.

Finding unexploded bombs dropped by the Allies over Germany is common even more than 65 years after the war's end. The explosives are usually defused or brought to a controlled explosion without causing injuries.

Officials had built a dam of hundreds of sand bags around the bomb site in the river bed to pump water out in preparation for the delicate task.

Train and road traffic has come to a halt in the area, some 130km northwest of Frankfurt. Seven nursing homes, two hospitals and a prison with some 200 inmates in Koblenz were also evacuated.

Several hundred city officials went from door to door on Sunday morning, ringing the bells to check whether any residents had failed to evacuate the area.

The residents of Koblenz, which was heavily bombarded during WWII, are somewhat used to bomb scares. City officials said 28 smaller war bombs had been found there since 1999, the German news agency dapd reported.

Such WWII bombs in Germany are often found during construction work or by farmers plowing their fields.