Emergency teams in the Balkans are shoring up flood defences along the River Danube and its tributaries, but many homes have already been swamped.
Soldiers built sandbag walls in Fetesti, south-east Romania
Several thousand people have been evacuated from their homes in Serbia, Romania and Bulgaria.
The floods were caused by melting snow and heavy rainfall.
The Danube has reached its highest level since 1895 in Romania, where some farmland and forest areas have been deliberately flooded to protect towns.
The floods have caused huge economic damage in the region, but so far the losses are not on the same scale as last year or 2002 - the year that severe floods wreaked havoc in Central Europe.
In Romania, the authorities hope the volume of water will reach its peak in the next day or two. But flood defences have been weakened in many places by nearly a week of high waters and the villages of Rast and Negoi are now submerged.
The Sava, Tisa and Tamis rivers have also reached dangerous levels.
In the Serbian town of Smederevo, about 40 kilometres (24 miles) east of the capital Belgrade, the Danube swamped a medieval fortress and railway line before being blocked by a barricade of sandbags and soil.
Floods in the Balkans last year left dozens of people dead and farmland and infrastructure damaged or destroyed.
This year many people had time to reinforce flood barriers as the rivers rose steadily, the BBC's Nick Thorpe reports from Budapest.
The deliberate flooding of some 100,000 hectares (247,000 acres) of rural land has had some success in Romania, he says.
Romanian agriculture ministry spokesman Adrian Tsibu told the BBC that some of these areas may be left as wetland, which was their original state before land was reclaimed.
In other developments:
- Dozens of buildings were damaged in Belgrade, low-lying areas of which were flooded
- In Bulgaria about 40% of the Danube port of Nikopol has been flooded and a tent city with space for 1,200 people has been set up near Vidin
- Romanian soldiers built sandbag walls in the south-eastern town of Fetesti, after dykes were breached in several places.
The Danube is now flowing at nearly 16,000 cubic metres a second, more than twice the normal volume in April.
Many low-lying streets have been flooded in Belgrade
The floods could delay crop-sowing in northern Serbia and other areas, agricultural economist Bill Slee told the BBC.
The head of the Danube Commission, which manages navigation on the Danube, said he was "surprised" by the river's high level.
"It's incredible, it's the first time in the history of our great river, and that's why we are preparing a [flood-prevention] plan for the future," Daniel Nedialkov told the BBC's World Today programme.
Zvonko Kostic, a waterways official in Smederevo quoted by the Associated Press, said few Serbian towns outside Belgrade had the heavy machinery necessary to shore up flood defences round-the-clock.
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