Serbia has asked Hungary to send ice-breakers to clear the Danube river after large chunks of ice formed during the past week of extremely low temperatures.
Authorities said they have declared an emergency situation along a stretch of the Danube near the Hungarian border. A Hungarian ice-breaker could arrive on Monday.
River traffic along the Danube - one of Europe's main waterways - has largely been suspended in eastern Europe during the cold spell.
Other rivers and lakes throughout the region have also been covered in ice.
Temperatures have risen above freezing in Serbia but more bad weather is expected next week.