German Chancellor Angela Merkel praised rescue efforts on her third trip to water-logged regions Monday as central Europe grappled with historic floods that have killed at least 19 people.

Parts of north Germany remain threatened by the swollen River Elbe where a dyke was breached overnight in Saxony-Anhalt state, adding hundreds more to the many thousands of residents already evacuated in the country.

"We know of course that the damage will be in the billions," Merkel said on a visit to Wittenberge, in Brandenburg state, after last week pledging immediate aid of 100 million euros ($132 million) as the deluge hit region after region.

Ironically under sunny skies, Merkel said the full extent of the damage had to be established as she spoke to volunteers racing to fill sandbags, calling the work of teams who have mobilised "impressive".

"One can be rather proud of our country when one sees how the people are pulling together in such a difficult hour," Merkel commented, after last week also visiting four other flood-hit states.

The torrent of flood waters in Germany has turned vast areas into a sea of brown water and sparked a mass mobilisation of emergency workers, as well as what Merkel's spokesman said was the biggest ever army deployment in the country.

The bursting of a dyke in Fischbeck, where a torrent of the Elbe forced a 50-metre long crack, showed the situation was still especially tense in places, with 2,500 people evacuated according to a local emergency task force.

The impact from the flooding on a railway bridge led to disruptions Monday in high-speed services between Berlin and the cities of Hanover and Frankfurt, Germany's Deutsche Bahn rail service said.

In Magdeburg where more than 23,000 people had been told to leave their homes, the historically high levels of the Elbe from Sunday were falling faster than expected but authorities remained prudent.

"There's a slight gasp of relief but still no relaxation," city council member Klaus Puchta said.

Water levels dropped to 7.12 metres early Monday after reaching a historic high of 7.46 metres on Sunday -- nearly four times its normal level and exceeding that of previous record floods of 2002.

Towns including Lauenburg and the village of Hitzacker in Lower Saxony were preparing for the peak to hit in coming days.

After fearing the worst, Hungary breathed a sigh of relief Monday as flood defences held firm, averting the worst of the floods, and the mighty River Danube began to recede after reaching a historic high.

"Budapest should be out of danger by Wednesday, and hopes to present a faultless record -- no deaths or injuries due to the flood," Prime Minister Viktor Orban said, adding the focus of defence efforts now moved to high-risk locations in the south.

After the Danube in Budapest reached a historic peak of 8.91 metres (29 feet) on Sunday evening, the water level began to fall early Monday.

But the Suzuki car plant in Esztergom, 65 kilometres (40 miles) north of Budapest, said many workers were unable to travel to work and production was halted on Monday but would resume Tuesday.

The deluge has also sparked massive emergency responses in Austria, where the death toll has now reached five, and Slovakia. Across central Europe, the floods have killed at least 19 people, including 10 in the Czech Republic.

The rains have also severely swelled the Danube in southern Germany, especially the city of Passau, which has moved from alert to clean-up mode.

Adding to tensions was a threat to attack dykes from a group calling itself the "Germanophobic Flood Brigade". Aerial and ground surveillance had been stepped up, said Saxony-Anhalt state interior minister Holger Stahlknecht.

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