About 45,000 people were being evacuated from their homes in the western German city of Koblenz Sunday ahead of work to defuse a World War II bomb, officials said.
The 1.8-tonne British bomb was discovered in the River Rhine after water levels fell. It was due to be de-activated later Sunday.
People living within a 1.8-kilometre (one-mile) radius of the site were ordered to leave their homes by 0800 GMT, the fire service said.
Some 2,500 fire, police, medical and technical personnel as well as city officials are involved in organising the evacuation, the biggest in Koblenz since World War II.
Nearly half the population of the city is affected.
Two hospitals, seven old people’s homes, a prison and several hotels have also been evacuated. Streets have been closed off and the main train station was shut to trains in the early morning.
The British bomb was discovered on November 20, together with a 125-kilogramme (275-pound) US bomb which was also due to be de-activated later Sunday as soon as officials confirm all buildings are empty.
More than six decades after the war, authorities believe there are still some 3,000 bombs buried beneath the capital Berlin alone, and unexploded devices are regularly discovered in construction work.
In June 2010, a 500-kilo Allied bomb, thought to be British, exploded and killed three German sappers and seriously injured two others in the central city of Goettingen as they prepared to defuse it.
