MAGLAJ, Bosnia — Packed into buses, boats and helicopters, carrying nothing but a handful of belongings, tens of thousands fled their homes Saturday in Bosnia and Serbia, seeking to escape the worst flooding in a century.
Authorities said 20 people have died but warned the death toll could rise further.
Three months' worth of rain has fallen on the region in just three days, creating floods that meteorologists say are the worst since records began 120 years ago.
Observed from the air, almost a third of Bosnia, mostly its northeast corner, resembled a huge muddy lake, with houses, roads and rail lines submerged under water. Admir Malagic, a spokesman for Bosnia's Security Ministry, said about a million people, or over a quarter of the country's population, live in the affected area.
Surging water reached up to the second floors of homes at times, sweeping away traffic lights and signs as it coursed through villages and towns in the two neighboring countries. Roads were blocked and metal bridges crumbled at the onslaught.
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.
"We need everything, we are underwater," mayor Mico Micic said as he appealed for help.
The soaking rain also caused nearly 300 landslides in Bosnia, burying dozens of houses and cars and further complicating relief efforts.
"They come unannounced in just a few seconds," said Fahrudin Solak, a Civil Protection official.
Mines from Bosnia's 1992-95 war have littered its mountains for decades but the landslides swept away many of the carefully placed mine field warning signs, increasing the risk of deadly accidents.
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, people had to be rescued by helicopter from their roofs.
Many in Bosnia lost homes they had only just rebuilt after the war, which claimed 100,000 lives and devastated the impoverished country.
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. Authorities also ordered residents of another nearby small town, Baric, to leave immediately Saturday afternoon. Many hurriedly climbed into buses and military trucks to get away.
Officials said more than 15,000 people have been evacuated from the flood-hit regions in Serbia, many finding shelter in schools and sports halls. Lines of mattresses covered the floors of Belgrade schools, with frightened survivors describing unstoppable torrents that surged in a matter of minutes.
"It's all gone, all that we worked for, our animals, everything," one sobbing woman told Studio B television.
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 and authorities urged residents to save energy to avoid brown-outs.
Prime Minister Aleksandar Vucic told a press conference that new wave of flooding 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 responded to government's appeal to build up flood defenses along the Sava. Bused in from all over the country, the volunteers worked around the clock, stacking up sandbag barricades with soldiers and emergency crews. The town of Sremska Mitrovica was a particular concern.
"You can feel the solidarity everywhere. People are doing everything they can. I am seeing children and older people shoveling sand and carrying sandbags and no one finds this labor hard," said volunteer Marinko Trivunovic.
"I'm proud of the fact that I'm from Belgrade and I've come here to help these people to save their homes. By saving this city, we're saving the whole country," said volunteer Nemanja Radovic.
International help poured into the two nations. A Russian team joined the rescue efforts in Serbia. Rescue teams from Luxembourg, Slovenia and Croatia were already in Bosnia, and others from the U.K., Austria and Macedonia were expected by the end of the day.
Residents in both countries mobilized through Facebook or other social media, collecting tons of food, blankets and clothing for the crisis-hit areas.
From the Italian Open in Rome, Serbia's best tennis player, Novak Djokovic, appealed for flood volunteers on his Twitter account.
"Support for everyone! Let's help the endangered! Join the aid action!" he tweeted.
Gec reported from Belgrade. Aida Cerkez and Sabina Niksic from Sarajevo, Bosnia; Irena Knezevic in Banja Luka, Bosnia; and Marko Drobnjakovic in Sremska Mitrovica, Serbia, contributed.