City authorities in Frankfurt plan to evacuate more than 60,000 people from their homes on Sunday to defuse a Second World War bomb found during construction work.
The 1.8-ton bomb of a type dropped by British bombers during the war was unearthed on Tuesday and contains 1.4 tons of explosives, city councillor Markus Frank said.
A radius of 1.5 kilometres (nearly a mile) around the bomb will have to be evacuated as a precaution ahead of the disposal itself, which is expected to take about four hours, Mr Frank said.
Officials are describing the planned evacuation as Germany's biggest yet, though similar operations are still common more than 70 years after the war ended.
In May, around 50,000 people had to leave their homes in Hannover temporarily for a bomb disposal.