Five people drowned as torrential rains flooded southern Bulgaria on Monday, breaking a dam wall and submerging a whole village under 2.5 metres of icy water, officials and rescuers said.

Three elderly men drowned in their houses in the village of Biser, in southeastern Bulgaria, mayor Zlatka Valkova told state BTA news agency.

National radio meanwhile reported that two more people died when their car was swept off a bridge into a swollen river near the southern village of Madzharovo.

The worst-hit regions of Haskovo and Svilengrad declared a state of emergency as floodwaters from the Arda and Maritsa rivers shut Bulgaria's major Kapitan Andreevo checkpoint on the border with Turkey.

Authorities warned both Turkey and Greece of massive floodwaters coming down along the two rivers.

A major rescue operation was underway in the worst-hit village of Biser, where floodwater reached up to the houses' rooftops.

“People are in panic. Ninety percent of the village is underwater,” regional mayor Mihail Liskov said on the radio.

Several teams of emergency workers, a special army unit and helicopters were battling to evacuate its 800 trapped inhabitants as many houses remained only accessible by boats.

Civil defence force chief Nikolay Nikolov warned that several smaller and two bigger dams in southern Bulgaria - Ivaylovgrad and Studena - were on the brink of overflowing and that people in the region should also be ready to evacuate.

Landslides meanwhile derailed the locomotive of a train from Belgrade to Istanbul near Svilengrad on the Turkish border, causing no injuries but leaving at least a dozen foreigners stuck for more than six hours.

A code red alert for stormy weather was declared in two regions in the Rhodope mountains to the south.

The village of Nedelino there remained in a state of emergency for a second day on Monday against massive landslides. The region was drenched by more than 100 litres of rain per square metre in just 24 hours on Sunday.

Weather services meanwhile forecast that an expected drop in temperatures to minus 17 degrees Celsius (1.4 Fahrenheit) this week will yield snowstorms over the coming days.

A cold snap since late January, also gripping large parts of Europe, with temperatures as low as minus 31.4 degrees Celsius (minus 24.5 Fahrenheit) has left more than 16 people dead in Bulgaria, local media reported. - AFP