In Serbia, the Danube and other major rivers eased slightly on Sunday, but local flood defence teams continued strengthening embankments in preparation for new floodwaters.
The Romanian government has ordered controlled flooding of thousands of acres of farmland to keep water out of populated areas.
Hundreds of residents were evacuated in the country’s south after a dam collapse threatened more than 130 homes.
An emergency camp is being set up on the outskirts of the northwestern Bulgarian city of Vidin.
In Belgrade and Smederevo, a town about 40km east of the Serbian capital, sand-filled trucks and fire engines worked to build up new embankments on the Danube, local radio reported.
The level of the Danube there reached 8.45m, around 40cm more than the highest level ever recorded, and it was expected to continue rising.
The Danube is Europe’s second-longest river. Rapidly melting snow and heavy rains have caused the record high levels and flooding.
At least 500 homes in towns and villages along the river were under water and the inhabitants forced to evacuate.
The river had already reached 9.75m in the eastern Serbian town of Veliko Gradiste, where the river makes a natural border with Romania, but defence teams have so far managed to prevent floods there.
In the nearby town of Golubac, where water had already inundated the bus station, school, hotel and pedestrian zone in the city centre, water pumps worked constantly and hundreds of people, including police and army units, filled bags with sand to rebuild defence dykes.
A strong wind put pressure on embankments and the weather bureau forecast that the river would rise another 30cm.
Meteorologists predicted the flooding would peak on Monday or Tuesday.
In Belgrade, where the Danube meets the Sava river, water levels rose more slowly than previous days.
But city authorities were forced to suspend traffic on several low-lying boulevards that have been covered with water for several days.
A part of Belgrade railway station was also flooded and hundreds of inhabitants were evacuated.
The severe flooding across the region is being caused by heavy rains and the spring melting of snow.
In Romania several villages were flooded and at least 100 people were evacuated. So far 700 people have been forced to leave their homes and around 500 households have been destroyed by the floodwaters.
In a bid to limit the damage in densely populated areas, authorities have decided to carry out controlled flooding over some 92,000ha of agricultural fields in three southern regions.
Romanian Prime Minister Calin Tariceanu and Environment Minister Sulfina Barbu visited two regions where this is due to be done to reassure citizens.
Weather forecasters said Romania should experience some relief by Monday as the levels of the Danube will begin falling there.
Neighbouring Bulgaria maintained a state of emergency in all seven regions which border the Danube.