WARSAW • More than 60 people have died in recent days as sub-zero temperatures sweep across swathes of Europe - notably, in Poland, Romania and the Balkans - with migrants and the homeless among the most vulnerable, officials said.

Six people died in Poland and seven more in the Balkans over a 24-hour period as temperatures plunged across Europe, while Romania announced six deaths in recent days.

The authorities in Warsaw said the hypothermia death toll in the country since Nov 1 has risen to 71.

Polish police urged people to help those most vulnerable, especially the homeless, as the mercury sank below minus 20 deg C in some regions.

"Another six people died due to exposure over the last 24 hours," Poland's Government Centre for Security said on Tuesday in a statement.

The local authorities have also issued smog alerts across Poland, urging children and the elderly to remain indoors as coal- and waste-fired home furnaces drove up air pollution to the highest levels recorded in years.

Last winter was unusually mild but still claimed 77 lives in the nation of 38 million, compared with the death tolls of 78 and 177 in the two preceding winters.

In the Balkans, a father and son were among at least seven people reported to have died in the last 24 hours, local media said - three each in Serbia and Macedonia, and one in Albania.

In southern Serbia, where temperatures have fallen below minus 20 deg C and a state of emergency has been declared, an 88-year-old father and his 64-year-old son died of cold in the village of Duga Poljana.

But in the east of the country there was rare good news as national television station RTS reported the miraculous survival of a man in the village of Smoljinac, who survived for two days in temperatures reaching minus 20 deg C after falling down a well.

In Slovakia, six people have succumbed to the weather in recent days, the country's Central Emergency Services said on Tuesday.

The current deep freeze sweeping Europe has also killed six people in Romania, according to the first official figures released by the Health Ministry in Bucharest.

This raises the total number of deaths across the continent to more than 60 in just a few days, with many of the victims being migrants or homeless people.

In Greece, which has more than 60,000 refugees, mainly from Syria, on its territory, many migrants have been moved to prefabricated houses and heated tents.

Greece has also sent a tank landing craft to the island of Lesbos, to pick up refugees and migrants currently living in miserable conditions in the Moria refugee camp, navy spokesman Spyridon Pollatos told Agence France-Presse.

AGENCE FRANCE-PRESSE