A state of emergency was declared across much of the Balkans today as the Danube, swollen by heavy rain and the spring snow melt, rose to a 111-year high.

Mass evacuations were being planned in riverside towns for 1,000 miles from the north-west tip of Serbia-Montenegro, through its neighbour Romania to coastal Bulgaria.

Authorities are optimistic that water levels will subside in the coming week but fears are growing over the health risks caused by sewage and mosquitos.

In Belgrade, the Serbian capital, low-lying streets are underwater and the city's ancient fortress has flooded. Hundreds of thousands of hectares of crops have been deliberately submerged in controlled floods to spare the downstream settlements.

In Romania, the Danube's banks have crumbled under the river's fierce torrent: water flowed at a record rate of 15,900 cubic metres per second, double the normal flow of 7,900 cubic metres per second. At least 1,000 people have been evacuated from their homes.

"We are going through an unprecedented situation. Romania has never had such water levels," said Madalin Mihailovici, director of the Agency for Romanian Waters.

Officials have commandeered tractors, bulldozers and other vehicles, but in many places damage from floods which claimed dozens of lives last summer has yet to be fully repaired.

The Romanian-Serbian border region, where the Danube forms the frontier between the two countries, has been badly hit. In the town of Bazias, the heavy rains and melting snow triggered a flood that covered 5,000 hectares (12,400 acres) on the Danube’s northern bank.

A number of victims of last year's floods in the west county of Timis have had their replacement homes destroyed.

In Serbia, officials declared a state of emergency in ten regions as all four of its rivers, the Danube, the Sava, the Tisa and the Tamis, rose to record levels. Thousands of troops were deployed to build up defences against the waters and stack sandbags along the riverbanks.

The Agriculture Ministry said that 223,000 hectares (550,000 acres) were under water. Parts of Belgrade, where the Danube meets the Sava, have been flooded for days, and telephones in riverside areas have stopped working.

In the eastern town of Smederevo, authorities drafted all men employed in the municipal services to flood-fighting crews on the Danube. Dozens of people were evacuated to a refugee centre and 5,000 acres of fertile farmland surrounding the town were flooded.

Zvonko Kostic, a waterways official in Smederevo, stressed that few Serbian towns and cities, except for Belgrade, have the necessary heavy machinery required to fight floods around the clock. "The volunteers are tired, it’s hard to keep up the tempo day after day," he said.

Villagers in Ritopek, nine miles southeast of Belgrade, were angered by the level of government help. "The state has practically forgotten us. All they did was bring a truckload of sand and dump it here," resident Andra Miletic told AP.

In Bulgaria, the ports in Lom, Oryahovo and Somovit were submerged with locals taking to boats. In Vidin, on the north-west tip of the country, 1,200 have been evacuated to a tented city after the Danube's waters reached a record 9.4 metres. All 50,000 of the town's inhabitants have been put on standby to leave.

To the east in Nikopol, largely under water on Saturday, the river had receded this morning but soldiers and divers continued to fortify dykes.

They said although the river should fall slightly on Monday and Tuesday, they were not out of danger as the flood now in Serbia was expected to reach the area and push waters higher again in the middle of the week.

"I expect the most significant rise of the water level on Wednesday. I’m afraid the high water could last up to a month," said Georgi Linkov, the head of regional civil defence for Nikopol."The biggest worry now is the inflow of mosquitos and the stink of sewage coming from the flooded houses."

Across the region residents have been left without power, transport or drinking water.

Despite the floods, Belgrade’s famed nightlife continued at the weekend. Srdan Jovanovic, the head of the city’s flood defence team, made an appeal to young women frequenting restaurants and clubs. He asked them to stop walking over the sandbags in their high-heeled shoes as they were puncturing the city’s flood defences.

THE DANUBE

It starts in the Black Forest in Germany and flows into the Danube Delta by the Black Sea

It is the second-longest river in Europe after the Volga, covering 2,850km (1,771 miles)

It touches ten countries: Germany, Austria, Slovakia, Hungary, Croatia, Serbia and Montenegro, Bulgaria, Romania, Moldova, and Ukraine

It flows through four capitals: Vienna, Bratislava, Budapest and Belgrade

In 2002 floods along the river killed 100 people and caused nearly c10 billion (£7 billion) in damage

A flood in 1965 destroyed 3,500 houses in Czechoslovakia and another in 1838 put most of Budapest under water

The Danube Delta is a World Heritage Site and home to the endangered pygmy cormorant

Rainwater from 815,800 sq km (315,000 square miles) of Europe drains into the Danube

The Blue Danube, the waltz by Johann Strauss, was written in 1867 while the composer was travelling along the river.

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