Soldiers and residents in southwestern Poland are laying sandbags near swollen rivers around the city of Wroclaw to protect homes and businesses after days of flooding across Central Europe.

By Janis Laizans and Radovan Stoklasa NYSA, Poland/OSTRAVA, Czech Republic (Reuters) -Poland's historic city of Wroclaw readied buses for possible evacuations on Tuesday and the zoo called for volunteers to protect animals from rising water as the death toll in three days of devastating floods across central Europe rose to 21.

Soldiers have dropped sandbags from military helicopters to reinforce river embankments and evacuated residents as the worst flooding in years spreads across Central Europe, taking lives and destroying homes.

Exceptionally heavy rainfall has been pounding Central Europe and has prompted deadly flooding in the region, with four new deaths reported in Poland, three in Czech Republic and one in Romania.

Volunteers in the Polish town of Nysa fortified floodwalls to stem swollen rivers on Tuesday after heavy rain and flooding round central Europe that has killed at least 18 people. Rivers were still spilling banks in the Czech Republic,

Poland's third-largest city Wroclaw was bracing for peaking flood waters on Thursday, with early indications its defences were holding firm, after the worst floods in at least two decades ravaged central Europe this week.

By Barbara Erling WROCLAW, Poland (Reuters) -Flood defences in Poland's third-largest city Wroclaw looked to have held firm on Thursday, after the worst floods in at least two decades ravaged central Europe this week.