BELGRADE, Serbia -- Tens of thousands fled their homes Saturday in Bosnia and Serbia, evacuated by boat or helicopter as rising waters surged into villages and towns. Authorities said the record flooding killed at least 20 people and the death toll could rise further.
Meteorologists say the flooding is the worst since records began 120 years ago and is due to a three-month amount of rain that fell on the region in just three days. Goran Mihajlovic from Serbia's Weather Center told The Associated Press that such a rainfall happens once in 100 years.
In the eastern Bosnian town of Bijeljina, some 10,000 people were being evacuated Saturday after the rain-swollen Sava River pushed through flood defenses. Mayor Mico Micic appealed for help, saying "we need everything, we are under water."
Officials in Bosnia say 12 people died and more bodies could emerge as water recedes from the dozens of cities flooded in the past three days. In some places, floodwaters had reached the second floor of people's homes and they had to be rescued by helicopter from their roofs.
In Serbia, which saw eight deaths, emergency crews and soldiers were using boats and helicopters to rescue thousands trapped in the town of Obrenovac, near Belgrade. Officials said more than 15,000 people have been evacuated so far from the flood-hit regions, most of them finding shelter in schools and sports halls.
The flooding in Obrenovac is threatening the Nikola Tesla power plant, Serbia's biggest. Plant capacity had already been cut after a nearby coal mine was flooded.
The rain eased in some parts Saturday but Prime Minister Aleksandar Vucic told a press conference that new flood wave on the Sava River will hit Sunday evening.
"Our primary concern is to protect the power plant," said Vucic. "We are doing all we can."
Thousands of volunteers have responded to government's appeal to help build up flood defenses along the Sava. Bused in from all over the country, the volunteers spent the night building sandbag barricades with soldiers and emergency crews.
One volunteer from Belgrade, Nemanja Radovic, came to Sremska Mitrovica, a town on the Sava.
"I've come here to help these people to save their homes," he said.
Both Serbia and Bosnia have appealed for international help. A Russian team has joined rescue efforts in Serbia and many European Union countries have sent in equipment and emergency crews.
In Bosnia, many lost homes they had only just rebuilt after the 1992-95 war, which claimed 100,000 lives and devastated the impoverished country. Scores of landslides hit as sodden hills gave way, also presenting a huge problem.
"They come unannounced in just a few seconds," said Fahrudin Solak, Civil Protection official, said of the landslides.
Residents in both countries have mobilized through Facebook or other social media, collecting tons of food, blankets and clothing for the crisis-hit areas.