More than 50,000 residents from the southern German city of Augsburg are being evacuated from their homes so that an operation to defuse a World War Two bomb can get under way on Sunday.
It is the country’s biggest evacuation for an unexploded bomb since the end of the war.
The 1.8-tonne British explosive is thought to have come from a 1944 air raid, which destroyed the old town.
It was uncovered during construction work.
Police say they do not know how long the operation will take.
The BBC’s Europe regional editor Mike Sanders said the city authorities are taking no chances, and are evacuating everyone with a 1.5km (one mile) radius of the bomb.
The authorities are confident that most people affected can stay with friends or family, but a number of schools and sports halls have been opened as shelters for those in need.
Most Germans celebrating Christmas open their presents and have their main festive meal on 24 December, rather than Christmas Day.
Other WW2 bombs recently discovered in Germany
- May 2015: 20,000 people in Cologne forced to leave their homes after a one-tonne bomb was discovered
- January 2012: A construction worker was killed when his digger hit an unexploded bomb in Euskirchen.
- December 2011: 45,000 people were evacuated from Koblenz after two bombs were found in the riverbed of the Rhine. It took three hours to make them both safe.
- June 2010: Three members of a bomb disposal squad were killed in Goettingen during an operation to defuse a bomb found on a building site.