Raging waters from three rivers have flooded large parts of the south-east German town of Passau following days of heavy rainfall in central Europe.
A spokesman for the city's crisis centre said the situation was "extremely dramatic" and waters are expected to rise further by midday to their level highest in 70 years.
Much of the city is reportedly only accessible by boat and there are power outages in some areas.
At least four people have reportedly died and nine are missing due to floods in Germany, Austria, Switzerland and the Czech Republic in recent days.
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Passengers, including a pregnant woman, say they have been stranded since 4pm yesterday.
The boxer said it was the "least he could do" and even donated the £30,000 shorts he wore in his last fight against Devon Alexander.
By Sunday it should become drier with spells of winter sunshine but temperatures will still remain on the cool side.