Serbia’s main power plant is being threatened by the worst floods in the Balkans for decades, officials say.

The River Sava has burst its banks in many areas and water levels are expected to peak later on Sunday.

At least 20 people have died in Serbia and Bosnia-Herzegovina after a month’s worth of rain fell in three days, and the death toll is expected to rise.

In Bosnia, landslides have buried houses and disturbed landmines laid during the war in the 1990s.

The floods are also affecting Croatia.

In Serbia, thousands of residents in Obrenovac were moved to safety after much of the town was inundated.

The town, south-west of the capital Belgrade, is home to the Nikola Tesla power plant, which supplies much of the country.

Serbian PM Aleksandar Vucic said that his government’s primary concern was to protect the power plant.

“We are doing all we can,” he said.

Thousands of volunteers have responded to the government’s appeal to build up flood defenses along the Sava.

Serbian tennis player Novak Djokovic also appealed for help.

“Support for everyone! Let’s help those in danger! Join the aid action!” he wrote on his Twitter account.

Officials have refused to give a death toll for Obrenovac until the floodwaters recede.

Almost one-third of Bosnia is under water. The north-east is worst affected, with houses, roads and railway lines submerged.

Bosnian Serb police chief Gojko Vasic said the situation had been particularly difficult in Doboj “because the flood waters acted as a tsunami, three to four metres high”, the Reuters news agency reported.

Bosnian Security Ministry spokesman Admir Malagic said that about one million people – more than a quarter of the country’s population – live in the affected area.

Chairman of the Bosnian three-man presidency Bakir Izetbegovic said that his country is facing a “horrible catastrophe”, the Associated Press reported.

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More than 20 people are feared dead in Bosnia-Herzegovina and Serbia after the worst floods in more than a century.

Tens of thousands of people have fled their homes as several months of rain fell in a few days and rivers burst their banks.

Landslides have buried houses in Bosnia and reports say as many as 16 people may have died.

An outer suburb of the Serb capital Belgrade has been inundated and eight people are reported to have drowned.

Serbian PM Aleksandar Vucic told reporters the first bodies had been recovered in Obrenovac, the worst-hit area to the south-west of the capital, and he feared more would be found.

But he said the number of deaths would not be made public until the waters had receded.

A new flood surge was expected on the Sava River late on Sunday, he said.

In some areas, flood waters reached the second floor of people’s homes.

“The flash floods woke my uncle at around 0330 so they went up to the first floor. Then they had to go to the third floor because all lower floors were flooded,” one resident from Obrenovac said.

Rescue workers have been working to bring thousands of stranded residents to safety and officials have also ordered the evacuation of another town, Baric, closer to Belgrade.

The Sava River has risen particularly high in the western town of Sabac, and volunteers have tried to shore up flood defenses there.

Rescue co-ordinator Predrag Maric appealed for food, water, and clothing to help those in need.

One of the worst-hit areas in Bosnia is the eastern town of Bijeljina where rescue teams are trying to transport 10,000 people to safety.

Among those who drowned were 10 people in the Bosnian Serb Republic, police told local media. Six bodies were found in the northern town of Doboj and there are fears that more people have lost their lives.

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