Slovenian authorities on Monday urged residents along the Drava to evacuate after the river started overflowing its banks following several days of heavy rain.

"The red alert is in force along the Drava river... We urge citizens to follow the situation and instructions of the defence and rescue teams," the country's Environment Agency said Monday after declaring the highest degree of flood danger.

Following the agency's warning, local media in several towns and villages on the banks of the Drava river called citizens to evacuate to safer areas.

"The Drava river is overflowing its banks over its entire length... We expect high levels to remain all night from Monday to Tuesday," the head of the Environment Agency Janez Polajnar told an emergency news conference on Monday afternoon.

He added the situation was critical also in eastern Slovenia where the Krka river started inundating its surroundings near its confluence with the Sava river on the border with Croatia.

"We expect the wave of high levels on the (Drava and Sava) rivers to move overnight and on Tuesday towards Croatia," Polajnar said, warning citizens the situation would remain critical over the following 24 hours.

Slovenian media reported some areas of the country's second-largest city Maribor, which is on the Drava, had been inundated on Monday while the floods also interrupted or damaged the road communications with the towns of Dravograd and Slovenj Gradec, close to the border with Austria.