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, officials said Sunday.

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.

A resident located north of Budapest looks out from her home. (Bernadett Szabo/Reuters)

The neighbourhood 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 neighbourhood's dewatering pumps.

Dam threat

Another 8,000 people had been evacuated from the town of Aken and its neighbouring 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 defences 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 48 kilometres 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.