BUCHAREST, Romania — Officials suspended shipping along Europe’s second-longest waterway on Tuesday as a polar spell gripped a large swath of the continent, causing hardship especially among migrants, the homeless and the elderly.

The deep freeze has caused at least 61 deaths since it began last week, a third of those in Poland.

Romanian police halted shipping at midday for an undetermined period along a 565-mile stretch of the Danube River, which crosses Romania. Croatian and Serbian authorities also stopped river traffic on the Danube.

In Serbia, shipping was banned on the River Sava because of icy conditions, which claimed another two lives in southern Serbia.

Authorities said an 88-year-old man and his son, 64, died from freezing temperatures in the village of Duga Poljana, in the south, which has been hardest-hit by the recent cold spell. Serbian state TV reported the two victims, discovered by a man delivering bread from a neighboring village, were extremely poor.

Three people have been found dead in the past three days in Macedonia as temperatures plunged to minus 20 degrees. One 68-year old homeless man was found frozen to death in the capital, Skopje, while a 60-year-old man died in front of his home in the southern town in Strumica. An 80-year-old woman was discovered in her home in eastern Macedonia.

Authorities urged homeless people to go to shelters and local schools.

In Albania, it snowed in the southern city of Saranda for the first time in 32 years. A homeless Albanian man was found dead in the southeastern city of Korca, the fifth person to die in the frigid weather.

In central town of Bulqize, temperatures plummeted to minus 22 degrees, with most rural areas cut off by snow. There were temporary power and water outages. Army helicopters were distributing aid in remote mountain areas.

After strong criticism from aid agencies and others, authorities on the Greek island of Lesbos said they would move 250 refugees from tents at camps into vacant hotel rooms as heavy snow continued unabated around the country.

The government also said it was sending a Greek navy ship to Lesbos, to serve as a floating shelter for residents of a snow-bound camp.

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