BUDAPEST -- This city's embrace of the Danube, which normally bisects Budapest as a gently rolling swath of silver, turned threatening on Sunday when the river spilled over its banks and claimed the Hungarian capital as the latest victim of record floods in Central and Eastern Europe.
An unusually wet spring has swollen the Danube, the Elbe and several of their tributaries across Austria, the Czech Republic, Germany and Hungary, forcing the evacuation of tens of thousands of people, disrupting rail and road traffic, and causing damage that preliminary estimates have predicted will reach several billion euros.
The authorities in Budapest had declared a state of emergency last Tuesday, anticipating that water level would reach record highs in the north of the country. The Danube was expected to peak at 8.95 meters, or about 29 feet, Sunday night or Monday morning.
Hungary deployed 7,000 soldiers supported by several thousand volunteers to reinforce dikes along the river. Hungarian state television showed Prime Minister Viktor Orban at work near the city of Esztergom, north of Budapest.
"The flood is approaching the heart of the country, Budapest," Mr. Orban told reporters on Sunday. "The next two days will be decisive, because the danger will affect the place where the largest number of people live and the most valuables are at risk."
In the eastern German city of Magdeburg, the waters of the Elbe rose faster and higher than expected. The authorities asked more than 23,000 people to leave their homes as the waters reached 7.46 meters on Sunday.
The authorities monitored dikes along the flood route, which stretched 40 kilometers, or 25 miles, by Sunday. Already strained by the task or reinforcing sodden dikes with thousands of sandbags, emergency officials had a new concern on Sunday when a group calling itself the Germanophobe Flood Brigade threatened in a letter to attack the barriers.
Holger Stahlknecht, the top security official for the state of Saxony-Anhalt, ordered more helicopters to patrol the skies above the flooded area and increased security along the dikes, telling the German news agency DPA, "We are taking the letter seriously."
Germans from across the country responded to calls over social networking sites to organize and help the efforts to protect threatened areas, winning praise from President Joachim Gauck, who toured the flooded areas on Sunday.
In 1997, less than a decade after the reunification of East and West Germany, record flooding along the Oder River became a rallying point for the newly minted nation.
"Germany is a country of solidarity," Mr. Gauck said after meeting several of the thousands of people from the country's former east and west who flocked to stricken villages along the Elbe to help fill and pile the thousands of sandbags needed to hold back the rising waters.
In Hungary on Sunday, road and rail traffic was restricted in Budapest and other areas along the river, although the authorities suggested that despite the flooding, most of the capital would stay largely dry. About 1,200 people had been evacuated throughout the country
Officials said dikes would have to be protected for about a week until the flooding fully subsides. This year's flooding on the Danube has already surpassed water levels measured in 2006, when all of Hungary's major rivers swelled beyond their banks, causing 25 billion forints, or about $110 million, in damage.
In recent years, specialists have warned repeatedly of the danger and cost of the failure to develop a comprehensive flood defense system for the country.
The national water authority declined to comment on Sunday, but an assessment published on their Web site found that decreased drainage capacity of the Hungarian flood protection system was due largely to increased building on former floodplains along the country's rivers.
The European Environmental Agency on Wednesday warned that flooding was likely to increase in Europe in the future, citing several reasons, including climate change, said Hans Bruyninckx, the agency's executive director.
"But in many cases," he said, "flood risk is also the result of where, and how, we choose to live."
Palko Karasz reported from Budapest and Melissa Eddy from Berlin.
This article originally appeared in The New York Times.