Hungarians have been warned to prepare for their country's worst floods ever as the Danube is set to reach record levels this weekend.
"We are facing the worst floods of all time," said PM Viktor Orban.
Europe's second-longest river is set to hit unprecedented levels in the capital Budapest in the next few days.
A state of emergency has been declared, and thousands of volunteers have been working to reinforce the banks of the swelling river.
Water levels are set to reach 8.85m (29ft), some 25cm (10in) higher than the Danube's previous record high in 2006.
Emergency workers have set up camps along the river as residents packed sandbags around their homes amid an atmosphere of concerned expectation, says the BBC's Nick Thorpe in Budapest.
Kristalina Georgieva, the EU Commissioner for International Co-operation, Humanitarian Aid and Crisis Response, tweeted: "Hungary well prepared for highest ever measured water levels on Danube. We are monitoring & ready to assist."
Mr Orban, who spent the night at a military barracks in the flooded western city of Gyor, said recent dry weather in Austria and Germany, as well as a hot forecast for Hungary over the weekend, gave reason to hope that Europe's worst river floods for more than a decade could soon be over.
"The fact is that along the border (where the Danube lies between Hungary and Slovakia) the water level is already above the highest level ever measured," he added.
Budapest Mayor Istvan Tarlos said that in a worst-case scenario up to 55,000 people may need to be evacuated.
However, he said he was confident that only the lowest-lying areas would be exposed to the river's expanded flow.
Nine hundred people have already had to evacuate their homes upstream, the Associated Press news agency reports.
Widespread flooding in central Europe has inundated swathes of Austria, Germany, Slovakia and the Czech Republic, killing at least 15 people.
In the Slovak capital Bratislava, the main flood defences held firm against the swelling Danube on Thursday.
But while river water levels were receding in some areas, the Danube had yet to reach its peak in Slovakia, said the European Commission's newly inaugurated Emergency Response Centre (ERC).
In northern Germany, workers piled sandbags along the banks of the River Elbe as waters rose, after widespread flooding further south.
As flood waters receded to the south and east, defence work continued apace near Lueneburg in Lower Saxony.
Tens of thousands of people have been evacuated from threatened areas in Germany, where the flooding is worse than that recorded in 2002.
The economic impact might be worse than the 11 billion-euro losses caused by the 2002 floods, said Eric Schweitzer, the president of the German chamber of trade and industry,
"In some regions, the extent of damage is likely to be rather larger than in 2002," wrote Mr Schweitzer in an editorial for the Rheinische Post newspaper.
On Thursday the Elbe flooded parts of Dresden as it peaked nearly 7m (22ft) above its normal level, but the city's historic centre remained unscathed.
Upstream along the Elbe in the Czech Republic, emergency workers used boats to shuttle supplies to stranded people as large areas remained under water.