An aerial view of the flooded areas near the Bosnian town of Brcko, along the river Sava, north of the Bosnian capital, Sarajevo. Picture: Bosnian Army

Sarajevo - Floodwaters slowly receded in the Balkans on Thursday after the region's deadliest natural disaster in living memory, revealing widespread devastation and allowing the mammoth task of cleaning up to begin.

The first evacuees got a green light to return home, among the 150 000 who fled as the Sava river burst its banks and laid waste to parts of Bosnia, Serbia and Croatia.

The death toll from the Balkans' worst floods in more than a century stands at 51, but could yet rise if more bodies are discovered in houses and farms swamped by the floods and landslides.

Vast tracts of farmland remain under muddy brown water, large areas are without power and many places are difficult to access. Those returning have been greeted by scenes of desolation and an unbearable stench.

“We need international aid. In this first phase alone people need clothes and food,” Igor Radojicic, parliamentary speaker in the Bosnian Serb entity Republika Srpska, told AFP.

“Lots of people are not going to have a home any more.”

The past week's floods affected more than 1.6 million people across the Balkans, with a quarter of Bosnia's population of 3.8 million without safe drinking water.

In Croatia, which escaped the worst damage, authorities said 38 000 people have been affected by the floods, with 2 000 houses and 199 farms destroyed.

With temperatures approaching 30 degrees Celsius, a major challenge remains clearing up drowned animals before their carcasses start to rot in the heat and potentially spread diseases.

In Serbia around 200 tons of dead animals have been recovered so far, the agriculture ministry said. Health officials were also spraying to try to prevent a plague of mosquitoes.

Complicating the operation in Bosnia is the danger that the floods and landslides could have dislodged some of the 120 000 potentially deadly landmines left over from the Yugoslav wars of the 1990s.

On Tuesday one such device exploded in northern Bosnia, the national Mine Action Centre (MAC) said, although no one was injured. A fridge full of explosives and a rocket-launcher thought to date from the conflict were also recovered.

“Some mines are made of plastic and they float like plastic plates,” said Fikret Smajis from the MAC. “But even those made of iron... can be easily washed away.”

Visiting Nato chief Anders Fogh Rasmussen said in Sarajevo on Wednesday that the members of the military alliance “remain ready to respond in any way that would be needed”.

Meanwhile, Serbia's Prime Minister Aleksandar Vucic was due to meet with officials from the World Bank, the European Bank for Reconstruction and Development (ERBD) and the United Nations to seek financial help.

Vucic has said that with hundreds of bridges damaged and 3 500km of roads needing repairs, the total bill could be as high as one billion euros.

The railway line linking Serbia to the Montenegrin port of Bar, of major importance to Serbia's economy, will remain unpassable for at least a month, making life difficult for a Fiat factory at Kragujevac.

In Bosnia, officials have estimated the damage bill could be hundreds of millions of euros, while in Croatia damages to agriculture alone were expected to reach at least 30 million euros.

“We will do as much as we can to help this region... The first thing is to have a good sense of needs in terms of reconstruction,” ERBD head Suma Chakrabarti said on Wednesday. - AFP