Snow drifts reaching up to rooftops kept tens of thousands of villagers prisoners in their own homes Saturday as the death toll from Europe's big freeze rose past 550.

More heavy snow fell on the Balkans and in Italy, while the Danube river, already closed to shipping for hundreds of kilometres because of thick ice, froze over in Bulgaria for the first time in 27 years.

Montenegro's capital of Podgorica was brought to a standstill by snow 50 centimetres deep, a 50-year record, closing the city's airport and halting rail services to Serbia because of an avalanche, AFP reported.

Eight more people were reported to have died in Romania, taking the toll for the country to 65, three in Serbia, one in the Czech Republic and one in Austria.

Polish fire brigade spokesman Pawel Fratcak said Saturday that defective heating had triggered a spate of deadly blazes in houses and apartments, with eight people killed on Friday night and three the night before.

New Romanian Prime Minister Mihai Razvan Ungureanu and his defence and interior ministers, who were sworn in only on Thursday, flew by helicopter to the eastern Buzau region, one of the worst hit, on Saturday.

He called on the authorities to work hard to beat the challenges facing them, as food threatened to run out in some villages in spite of air drops.

At Carligul Mic firemen and volunteers helped people dig tunnels and trenches in the snow reaching to the house roofs in some places.

Authorities said an estimated 30,000 people were still cut off in Romania, and more than 110,000 in the Balkan countries, including 60,000 in Montenegro, nearly 10 percent of the population.

Belgrade has taken steps to limit electricity consumption in the face of threatened shortages, calling on companies to reduce their activities to a minimum.

With Wednesday and Thursday already public holidays for Serbia's national day, the government has also declared Friday a non-working day to extend into next weekend.

Forecasters expect the cold snap, which started two weeks ago, to continue until mid-February.