Thousands crammed into boats and army trucks as they fled their homes in Serbia and Bosnia, after record rainfall turned the Sava river into a deadly torrent and caused the worst floods in the Balkans in more than a century.
Officials said on Sunday that the disaster has killed at least 44 people so far, and some towns had been completely cut off. Rescue teams feared the worst as they were finally able to move in.
Some 10,000 people have been evacuated so far from the worst-affected areas of northern Bosnia, but in some places like the town of Samac, hundreds of stranded people were still waiting to be rescued, according to news agency AFP.
"We sent rescue teams into a part of the city we had not been able to access so far. They are entering those areas fearing what they might discover," Mayor Samo Minic told reporters.
Al Jazeera's Nazanine Moshiri, reporting from the Serbian town of Obrenovac, said the massive logistical operation threatened to "completely overwhelm" Serbia's emergency services.
It was not clear how many people died in Obrenovac, but officials told our correspondent that they had to wait for water to recede to see what damage had been done.
"There are still many houses completely submerged by flooding and still many people waiting to be rescued," she said, adding that some residents had expressed anger that rescuers did not arrive earlier.
'Like a tsunami'
Rescuers who arrived found widespread devastation.
"It looks like a tsunami and earthquake occurred at once. Water carries everything. Corpses of animals could be seen floating everywhere," said Nedeljko Brankovic, who was among rescue workers who managed to reach the village of Krupanj in western Serbia after two days.
"We found 50 people gathered in the highest house. They had neither electricity nor drinking water," Brankovic said.
"Telephones did not work. We evacuated them 10 by 10 in a huge boat," he said.
Besides the flooding, the worst rainfall since records began in the late 19th century also caused landslides that brought more destruction and prompted a landmine warning.
Bosnia's de-mining agency said residents around the towns of Doboj, Maglaj and Olovo - which saw fierce fighting during the war in the 1990s - should be particularly wary of landmines that may have been dislodged by the floods.
Twenty of the 27 deaths recorded in Bosnia occurred in Doboj while on the other side of the Sava river, in Serbia, at least 16 bodies were found.
Croatia has also confirmed one casualty, as a result of bad weather that engulfed much of central and parts of eastern Europe at the weekend.
Ukraine's emergencies ministry said heavy rain and wind had cut power to about 100 villages, but no casualties had been reported.