At least 365 migrants and refugees have drowned in the past three days in the Mediterranean in six incidents.
The International Organization for Migration said the deaths make this November already six more times more deadly than the same month a year ago.
"This is really a calamity in plain sight," IOM spokesman Leonard Doyle told a news briefing in Geneva.
"We are seeing really tragic scenes of rubber rafts going under the seas in the Mediterranean in the middle of winter."
The latest drownings, mostly West Africans leaving Libya for Italy, bring migrant deaths in the Mediterranean so far this year to 4,636, he said.
There have been 1,000 more deaths this year among roughly half as many people trying to reach Europe by sea, with some 343,589 arrivals so far this year, against 728,926 last year at this point, according to IOM figures.
Meanwhile, the crew of the LE Samuel Beckett rescued 50 people from a rubber vessel off the coast of Libya.
This brings to 2,310 the number of people rescued by the Irish naval ship since it was deployed to the area on 23 September.
