At least 29 migrants died of hypothermia aboard Italian coastguard vessels after being picked up from an inflatable boat adrift near Libya, the mayor of the Italian island of Lampedusa said.

Two patrol boats picked up 105 migrants late yesterday from the boat drifting in extreme sea conditions, with waves as high as 8 metres and temperatures just a few degrees above zero, the coast guard said in a statement.

The migrants spent around 18 hours on the decks of one of the boats taking them toLampedusa, buffeted by high winds and spray. At least 29 died en route of hypothermia, Lampedusa's mayor, Giusi Nicolini, told Reuters.

The number of dead may still rise, she said. One migrant had been taken by helicopter to  Sicily in critical condition, and the second patrol boat has yet to reach port.

Nicolini blamed the closure of Italy's search-and-rescue mission, known as Mare Nostrum, last year for the tragedy. Since then no navy ships capable of keeping large numbers of migrants below deck have patrolled the waters near the Libyan coast.

"Mare Nostrum was an emergency solution to a humanitarian crisis, so closing it was a huge and intolerable step backward," Nicolini said in a telephone interview. Human rights groups repeatedly warned that ending the mission would endanger lives.

"The small patrol boats were completely swallowed by the waves during the trip back. If Mare Nostrum were still going, the migrants would have been given shelter inside a large ship within an hour."

The patrol boats sent from Lampedusa are small vessels that ride low to the water so crew members can pull people in. But they cannot accommodate many below deck.

Mare Nostrum was abandoned by Prime Minister Matteo Renzi's government partly due to public concern over the 114 million euro ($129 million) cost of the mission in its first year.

Now the European Union is running a border control operation called Triton, with fewer ships and a much smaller area of operations.

Civil war in Syria and anarchy in Libya swelled the number of people crossing theMediterranean last year. Many paid smugglers $1,000-$2,000 to travel.

The United Nations refugee agency says 160,000 seaborne migrants arrived in Italy by November 2014 and a further 40,000 in Greece. Thousands have died attempting the journey.

"To organised crime it's not important if people make it across the sea alive or dead," Nicolini said. "But now, without Mare Nostrum, it's as if no one, and not just the criminals, cares if they live or die."