Frankfurt city officials are warning Germany's financial capital could grind to a halt if residents ignore orders to vacate their homes to allow the defusing of a massive World War II bomb.
On Sunday, the city will evacuate some 60,000 people in the nation's biggest such manoeuvre since the war while officials disarm the British bomb discovered on a building site this week in Frankfurt's leafy Westend, where many wealthy bankers live.
Fire and police chiefs would use force and incarceration if necessary to clear the area.
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An uncontrolled explosion of the bomb would be big enough to flatten a city block, Frankfurt fire chief Reinhard Ries told reporters.
"This bomb has more than 1.4 tonnes of explosives," he said. "It's not just fragments that are the problem, but also the pressure that it creates that would dismantle all the buildings in a 100-metre radius."
The HC 4000 bomb is assumed to have been dropped by Britain's Royal Air Force during the 1939-45 war. Such finds are not unusual, but rarely are the unexploded bombs so large and in such a sensitive position.
The compulsory evacuation radius of 1.5km around the bomb includes police headquarters, two hospitals, transport systems and Germany's central bank storing NZ$100 million in gold reserves.
Officials on Friday called on Frankfurt's residents to clear the area by 8am on Sunday and warned the effort could take at least 12 hours.
Police said they couldn't begin defusing the bomb until they were sure everyone had left the area.
They would ring every doorbell and use heat-sensing technology from overhead helicopters to help them identify stragglers, they said.
Frankfurters can spend the day at shelters set up at the trade fair and the Jahrhunderthalle convention centre, police have said.
In addition, most museums are offering Frankfurt residents free entry on Sunday, and a few of them will open their doors earlier in the morning than usual, the city said on its website.