BERLIN — Thousands of people have been evacuated from their homes in a region of eastern Germany where the Elbe river has flooded and burst through a dam, while swollen Danube was approaching Budapest where soldiers and volunteers are building flood walls, officials said Sunday.

Parts of the south and north ends of the Hungarian capital are already under water, but the city's downtown area, including the parliament building and several large hotels near the river bank, are seemingly out of direct danger as flood walls were built to a height of 30.5 feet (9.30 meters).

Officials said nearly 8,000 volunteers and specialized crews in Budapest had strengthened flood walls by packing and placing one million sand bags and many are also monitoring defenses for any leaks.

At least 21 flood-related deaths have been reported in central Europe, as rivers such as the Danube, the Elbe and the Vlatava have overflowed after a week of heavy rains and caused extensive damage in central and southern Germany, the Czech Republic, Austria, Slovakia and Hungary.

The latest fatality was an 80-year-old man who died of a heart attack in Austria on Sunday while cleaning up debris caused by flooding, the German news agency dpa reported.

In Magdeburg, the state capital of Saxony-Anhalt in eastern Germany, more than 23,000 residents had to leave their homes Sunday afternoon after many streets and buildings were flooded and electricity was shut off, dpa said.

The neighborhood of Rothensee was especially hard-hit by the floods of the Elbe river – residents were being evacuated with tanks, trucks and buses.

"Rothensee is filling up like a bathtub," Germany army spokesman Andre Sabzog told dpa.

Around 700 soldiers were trying frantically to build a dam of sandbags around a power substation. A flooding of the substation would not only leave thousands of households without water, but also lead to a breakdown of the neighborhood's dewatering pumps.

Another 8,000 people had been evacuated from the town of Aken and its neighboring villages after a dam on the Elbe river broke Saturday, police spokesman Uwe Holz said.

Further north on the Elbe river, residents were trying to protect themselves from flooding by building levees along the banks of the rising waterway.

Officials in Saxony-Anhalt state also were investigating what appeared to be a threat to destroy dams.

Several media outlets said they had received a letter threatening to blow up dams on the Elbe river, Holger Stahlknecht, the state's interior minister, said Sunday.

"We are taking the letter seriously," he told dpa. He said authorities have stepped up their surveillance of dams and urged residents to remain calm.

In Hungary, officials said the flooded Danube River was expected to reach Budapest late Sunday, but that defenses should keep the water out of most of the capital.

Hungarian Prime Minister Viktor Orban said no casualties have been reported in his country, but that 7,000 soldiers and thousands of volunteers were packing sandbags on the banks of the Danube to shore up flood walls.

"The flood is now approaching Budapest, the heart of the country," Orban said in Esztergom, some 30 miles (48 kilometers) north of Budapest. "Two decisive days are ahead of us because the danger will be where most people live and where most things of value are at risk. It is now when we have to gather all our strength."

While no flood-related deaths or injuries have been reported in Hungary, some 1,400 people have been evacuated from towns and villages along the Danube, including over 200 in Budapest.

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Associated Press writer Pablo Gorondi contributed from Budapest, Hungary.

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  • The roof of a summer cottage mirrors in the flooded area near Doemitz at the river Elbe, northern Germany, Monday June 10, 2013. Weeks of heavy rain this spring have sent the Elbe, the Danube and other rivers such as the Vltava and the Saale overflowing their banks, causing extensive damage in central and southern Germany, the Czech Republic, Austria, Slovakia and Hungary. (AP Photo/dpa, Jens Buettner)

  • In this aerial view a dam is broken in Klein Rosenburg, at the Elbe river, eastern Germany, Sunday June 9, 2013. (AP Photo/dpa, Jens Wolf)

  • A tram stop is inundated on the lower embankment flooded by the River Danube in Budapest, Hungary, Sunday, June 9, 2013. (AP Photo/MTI, Janos Marjai)

  • Backdropped by the Royal Palace in the Castle of Buda and the Chain Bridge, trees stand on the lower embankment flooded by the River Danube in Budapest, Hungary, Sunday, June 9, 2013. (AP Photo/MTI, Janos Marjai)

  • Ducks swim past cars flooded by water from the Arga River in La Magdalena, northern Spain on Sunday, June 9, 2013. Heavy rain has lead to flooding in northern Spain over the past few days, especially in Navarra province. (AP Photo/Alvaro Barrientos)

  • An aerial view of the flooded River Danube with the Chain Bridge in the foreground and the Parliament building in the background, centre right, in Budapest, Hungary, Sunday, June 9, 2013. (AP Photo/MTI, Imre Kmetz)

  • The June 5, 2013 photo shows an aerial view of the Elbe river that has flooded the historical old town of Meissen, eastern Germany. (AP Photo/dpa,Patrick Pleul)

  • In this aerial view a broken dike is photographed in Fischbeck, Germany at the Elbe river Monday June 10, 2013. (AP Photo/dpa, JensWolf)

  • In this aerial view the village of Fischbeck is flooded by the Elbe river after a dike broke Monday June 10, 2013. (AP Photo/dpa,Jens Wolf)

  • A man stands in front of his house which is flooded by the water of the Danube river in Fischerdorf near Deggendorf, southern Germany, on June 11, 2013. (CHRISTOF STACHE/AFP/Getty Images)

  • Local volunteers help to stack sandbags to strengthen a flood barrier against encroaching floodwaters from the nearby Elbe river on June 11, 2013 at Sandau, Germany. (Photo by Sean Gallup/Getty Images)

  • A hover craft boat drives in a flooded area by the river Elbe near the enclosed village Fischbeck, central Germany, Tuesday, June 11, 2013. (AP Photo/Jens Meyer)

  • In this June, 3, 2013 file photo a flooded enclosure with a penguin is pictured in the zoo in Prague, Czech Republic. (AP Photo/CTK, Katerina Sulova, File)

  • A measuring stick shows the level of floodwaters at just under 10 meters next to a marker that shows the level reached during the 100-year-flood of 2002 in a street flooded by the nearby Elbe river in the historic city center on June 6, 2013 in Meissen, Germany. (Sean Gallup/Getty Images)

  • Rescue workers in a rubber boat pass through streets flooded by the nearby Elbe river in the historic city center on June 6, 2013 in Meissen, Germany. (Sean Gallup/Getty Images)

  • People fleeing their homes as the flood waters rose take refuge in a sports hall used as makeshift accomodations in Bitterfeld, eastern Germany, on June 6, 2013. (ODD ANDERSEN/AFP/Getty Images)

  • Water of the swollen Elbe river churns past the historic city center of Dresden, Germany on June 6, 2013. (Photo by Sean Gallup/Getty Images)

  • A beer garden stands under floodwaters of the swollen Elbe river in the city center of Dresden, Germany on June 6, 2013. (Photo by Sean Gallup/Getty Images)

  • Rescue forces in a lifeboat help residents in a house flooded by the swollen Danube river, while a small spotter-aircraft is flying over Fischerdorf, a suburb of the city Deggendorf, Germany on June 6, 2013. (Photo by Joerg Koch/Getty Images)

  • An aerial view shows a motorway junction partially flooded by water from the River Danube near the Bavarian village Deggendorf, southern Germany, on June 6, 2013. (CHRISTOF STACHE/AFP/Getty Images)

  • An aerial view shows summer houses flooded by water from the River Danube near the Bavarian village Deggendorf, southern Germany, on June 6, 2013. (CHRISTOF STACHE/AFP/Getty Images)

  • Neighbors visit one another in a street flooded by the nearby Elbe river in the historic city center of Meissen, Germany on June 6, 2013. (Photo by Sean Gallup/Getty Images)

  • An aerial view shows flooding at Bratislava's harbor and shopping district on the Danube river on June 6, 2013. (SAMUEL KUBANI/AFP/Getty Images)

  • A helper cleans the bank of the river Elbe in front of the historical bridge Blaues Wunder (Blue Miracle), left, in Dresden, eastern Germany, Thursday, June 6, 2013. (AP Photo/Jens Meyer)

  • Geese stand on the roof of a flooded house by the river Danube in Deggendorf, southern Germany, Thursday, June 6, 2013. (AP Photo/dpa, Armin Weigel)

  • The flooded river Elbe in front of the historical old town skyline in Dresden, eastern Germany, Thursday, June 6, 2013. (AP Photo/Jens Meyer)

  • A resident reacts in front of a flooded house at the river Elbe in Dresden, eastern Germany, Thursday, June 6, 2013. (AP Photo/Jens Meyer)

  • A child runs over a wall of sandbags at the river Elbe in Dresden, eastern Germany, Thursday, June 6, 2013. (AP Photo/Jens Meyer)

  • The flooded river Elbe flows along the valley and the historical bridge Blaues Wunder (Blue Miracle) photographed in Dresden, eastern Germany, Thursday, June 6, 2013. (AP Photo/Jens Meyer)

  • The street sign "Danube avenue" is flooded by the swollen River Danube in Budakalasz, just north of Budapest, Hungary, Thursday, June 6, 2013. (AP Photo/MTI,Balazs Mohai)

  • An aerial view of the flooding in Passau, Germany, photographed Monday June 3, 2013. (AP Photo/dpa, Peter Kneffel)

  • The floods of the river Elbe submerge a sports ground in Pirna, eastern Germany, on June 4, 2013. (JOHANNES EISELE/AFP/Getty Images)

  • Three men stand behind wooden panels erected to protect a restaurant against the floods of the river Elbe in Pirna, eastern Germany, on June 4, 2013. (JOHANNES EISELE/AFP/Getty Images)

  • German soldiers shovel mud off a street in Passau, Germany, Tuesday June 4, 2013. (AP Photo/dpa,Andreas Gebert)

  • An aerial view of the village Kresice flooded by the swollen river Elbe, 63 kilometres (39 miles) northwest of Prague on Tuesday, June 4, 2013. (AP Photo/CTK, Radek Petrasek)

  • Photo provided by the German government shows German Chancellor Angela Merkel in a helicopter as she watches the areas hit by floods between Dresden and Pirna, eastern Germany, Tuesday, June 4, 2013. (AP Photo/Bundesregierung, Steffen Kugler)

  • Restaurants are flooded on an Danube island after heavy rainfalls in Vienna, Austria, Tuesday, June 4, 2013. (AP Photo/Hans Punz)

  • A traffic sign looks out of the water in a flooded street of the city of Pirna, Germany, Tuesday, June 4, 2013. ( AP Photo/Markus Schreiber)

  • An aerial view of highways crossing fields flooded by the swollen river Vltava in southern suburbs of Prague on Tuesday, June 4, 2013. (AP Photo/CTK, Vit Simanek)

  • Two firemen cross a street in the village Zalezlice flooded by river Vltava, 36 kilometres (22 miles) north of Prague on Tuesday, June 4, 2013. (AP Photo/CTK, Michal Kamaryt)

  • Aerial view of the swollen River Danube at Csepel Island, in Southern Budapest, Hungary, Tuesday, June 4, 2013. (AP Photo/MTI,Tibor Illyes)

  • This picture made available Tuesday June 4, 2013, shows an aerial view of the swollen Vltava river and a flooded house near Stare Ouholice village near Kralupy nad Vltavou, about 35 km (21.7 miles) north of Prague, taken on Monday, June 3, 2013. (AP Photo/CTK, Vit Simanek)

  • Harbour buildings are flooded along the Danube river in Deggendorf, Germany Tuesday June 4, 2013. (AP Photo/dpa, Armin Weigel)

  • Rudolf (11) crosses the flooded market place of the city of Wehlen at river Elbe, Germany, Tuesday, June 4, 2013. (AP Photo/Markus Schreiber)

  • The market place is flooded by the river Elbe in the city of Wehlen, Germany, Tuesday, June 4, 2013. (AP Photo/Markus Schreiber)

  • Two people watch waters falling down the Vltava river cascade on the Orlik Dam, some 40 kilometers south of Prague, on Tuesday, June 4, 2013. About 1600 cubic meters of water per second were flowing from the cascade towards Prague, until the outflow was regulated and lowered gradually. (AP Photo/CTK, David Veis)

  • Two men in a boat paddle over the flooded market place of the city of Wehlen at the river Elbe in Germany, Tuesday, June 4, 2013. (AP Photo/Markus Schreiber)

  • General view of Passau, flooded by the rising River Danube on June 3, 2013 in Passau, Lower Bavaria, Germany. Heavy rains across portions of Germany are causing flooding and ruining crops, with the town of Passau, also known as Dreifluessestadt or 'City of Three Rivers' particularly affected by flooding from its proximity to rivers Danube, Inn and Ilz. (Photo by Johannes Simon/Getty Images)

  • A general view shows the town hall in the flooded center of Passau, southern Germany, Monday, June 3, 2013. (AP Photo/Matthias Schrader)

  • Members of the Red Cross make their way by boats in a flooded street in the center of Passau, southern Germany, Monday, June 3, 2013. (AP Photo/Matthias Schrader)

  • A general view shows the flooded center of Passau, southern Germany, on Monday, June 3, 2013. (AP Photo/Matthias Schrader)