An Italian corvette picked up dozens of migrants from a sinking rubber dinghy on Tuesday after the vessel was spotted by a naval helicopter.

While those who run into trouble during the perilous Mediterranean crossing usually send distress calls to the Italian coast guard, this time rescue workers had heard nothing and it was only due to chance that the patrol helicopter spotted the craft.

“We can say how many people arrive but we never know how many set off. It's rarer now because of the number of ships in the area, but it's sure there are shipwrecks no-one knows about,” IOM spokesman for Italy Flavio Di Giacomo told AFP.

Fifty-four people plucked from the water were brought to the Italian island of Lampedusa, but according to testimony from survivors, the craft had set off with between 117 and 120 people on board, all of them from sub-Saharan Africa.

Over 30 of the passengers were women, fewer than half of whom survived according to the testimony. One of those aboard saw her sister drown.

Two other migrants were rescued by helicopter, winched to safety after they were spotted near the dinghy, clutching a water butt to stay afloat.

According to the latest IOM figures compiled Wednesday, over 101,700 migrants have arrived in Italy by boat since the start of the year, while more than 2,040 others died in their bid to cross.

The official tally provided by the interior ministry showed that by the end of last month, 93,542 people had arrived – slightly up on the 87,915 people who arrived during the same period in 2014.

Rough seas off Libya were slowing departures slightly, however, easing the pace of rescue operations launched by the Italian coast guard and European border agency.