More than 50,000 residents from the German city of Augsburg have been evacuated from their homes so that a huge World War Two bomb can be defused.
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.
Officials chose Christmas Day for the evacuation because it was less difficult than on a normal working day.
The bomb was uncovered during construction work on Tuesday.
Police say they do not know how long the operation will take, but evacuees are not expected to be able to return home before the evening.
Augsburg mayor Kurt Gribi, speaking in a video posted on the city's Twitter account, called for "each person to verify that their relatives, parents and friends have found places to stay outside the [security] zone ... Look out for one another."
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.