An unexploded wartime bomb has forced around 60,000 people from their homes in Frankfurt - Germany's biggest evacuation since World War II.
Unexploded bombs are regularly found in German cities.
Among those moved to safety are prison inmates and hospital patients.
More than 60,000 people have been ordered to leave a radius of 1.5 kilometers (nearly a mile) around the site where the 1.8-ton British bomb will be disposed of Sunday.
A temporary evacuation centre has been set up at Frankfurt's trade fair site.
Helicopters with heat-sensing cameras circled to spot stragglers and police chiefs said they would use force if necessary to clear the area, warning that an uncontrolled explosion would be big enough to flatten a city block.
Bomb disposal experts will use a special system to try to unscrew the bomb's fuse from a safe distance.
A thousand firefighters and an undetermined number of police officers were assisting in the operation, the largest in Germany's post-war history.
They were dropped by the RAF and US Air Force during the war.
Some 2,000 tonnes of undetonated explosives continue to be located every year in Germany, more than 70 years after the end of World War II. British and American warplanes pummeled the country with 1.5 million tonnes of bombs that killed 600,000 people.
Those affected have been offered free entry to several of the city's museums, while shelters have also been opened for residents.