A heavy winter snowstorm pummelled parts of southeastern Europe on Thursday, leaving at least one person dead, snarling road and air traffic and leaving thousands without power.

In the hardest hit parts of northern Bulgaria, snow drifts piled five-feet (1.5-metres) deep, forcing officials to scramble hundreds of off-road vehicles to clear clogged roads and tow stranded cars.

Across the border, in Romania's Giurgiu region, about 2,000 people were evacuated after they were stranded overnight in their cars on dozens of snow-clogged roads.

One man died of hypothermia after snow smothered his car. Rescuers saved a woman in the same vehicle.

Also in Romania, a pregnant woman delivered her baby in an ambulance that was stuck in the snow.

Bulgaria, meanwhile, declared its highest "code red" alert across the country after hundreds of homes were left without power and air and road freight traffic was disrupted.

The government's emergency response committee warned people to avoid all travel, as the snow, which began falling Wednesday, continued throughout the day.

The region of Lovech in northern Bulgaria and two small municipalities to the northwest, Svoge and Godech, declared a state of emergency, while some 300 towns and villages across the country were left without electricity.

In southern and central Serbia, several villages were unreachable, while people were running out of food and medicine, the B92 television channel reported.

Bucharest's airports cancelled about 40 flights, and train services were severely disrupted. Four ports on the Danube river and the Black Sea were also closed due to strong winds.

The Romanian meteorological institute said heavy snowfalls and strong winds could persist until Friday at noon in two regions close to the Black Sea.