BERLIN (AP) -- 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 people have been killed by a week of flooding in central Europe, as rivers such as the Danube, the Elbe and the Vlatava have overflowed after 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 Germany's eastern state of Saxony-Anhalt, more than 8,000 people were evacuated by bus from the town of Aken and its neighboring villages after a dam on the Elbe river broke on Saturday, said police spokesman Uwe Holz.

In Magdeburg, the state's capital, more than 3,000 residents had to leave their homes after many streets and buildings were flooded and electricity was shut off, dpa 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.