|A woman carries her belongings past a police officer as some 60,000 people in Germany's financial capital are about to evacuate|
Bomb technicians had been scheduled to begin work shortly after noon (1000 GMT), but the fire department said there were delays as some people refused to leave.
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.
Around 60,000 people were ordered to leave in what was Germany’s biggest evacuation since the war, with more than a thousand emergency service workers helping to clear the area.
A steady flow of people filed into a temporary shelter at Frankfurt’s trade fair site, with bananas and beverages on offer. Others sat in cafes on the edge of the evacuation zone.
The device was found last week in the city’s leafy Westend neighbourhood, home to many wealthy bankers. The evacuation area includes the central bank where $70 billion in gold reserves are stored.
Police set up cordons around the evacuation area, which covered a radius of 1.5 km (roughly a mile).
Premature babies and intensive care patients had to be evacuated along with everyone else from two hospitals and rescue workers helped about 500 elderly people leave residences and care homes.
In Frankfurt, bomb disposal experts will use a special system to try and unscrew the fuses attached to the HC 4,000 bomb from a safe distance. If that fails, a water jet will be used to cut the fuses.
The bomb was dropped by Britain’s Royal Air Force during the 1939-45 war, city officials said. British and American warplanes pummelled the country with 1.5 million tonnes of bombs that killed 600,000 people. Officials estimate 15 percent of the bombs failed to explode, some burrowing six metres (yards) deep.
More than 2,000 tonnes of live bombs and munitions are found each year in Germany, even under buildings. In July, a kindergarten was evacuated after teachers discovered an unexploded World War Two bomb on a shelf among some toys.
Three police explosives experts in Goettingen were killed in 2010 while preparing to defuse a 1,000 lb (450 kg) bomb.
Roads and transport systems, including parts of the underground, were to remain closed during the work and for at least two hours after the bomb is defused, to allow patients to be transported back to hospitals.
Air traffic from Frankfurt airport could also be affected and small private planes, helicopters and drones were banned from the evacuation zone.
Museums were offering residents free entry on Sunday, and many hotels offered discounts.