A rescue operation is under way after a boat carrying an estimated 700 migrants capsized in Libyan waters, 120 miles south off Lampedusa.
Twenty-eight people have been reported rescued, while a number of bodies have been washed ashore in Libya.
The migrants reportedly fell overboard when they ran to draw the attention of a passing vessel. The boat is said to have capsized at midnight.
The disaster could become one of the worst over the decades of the migrant situation in the southern Mediterranean, which has seen the death toll rise over 1,500 since the beginning of 2015, Reuters reported.
“At the moment, we fear that this is a tragedy of really vast proportions,” Carlotta Sami, a spokeswoman for the UN High Commissioner for Refugees, told SkyTG24 television.
“The first details came from one of the survivors who spoke English and who said that at least 700 people, if not more, were on board,” Sami added.
A Maltese Navy spokesman told the BBC that Italian ships and commercial boats were also involved in the emergency operation.
In the next few hours, the operation will focus on the search for bodies.
A few days earlier, almost 400 migrants drowned in the Mediterranean as their boat carrying 550 people bound for Italy capsized approximately 24 hours after leaving Libya.
The flow of migrants has increased due to fine spring weather over the last few weeks.
About 20,000 migrants have made it to the Italian coast this year, according to estimates by the International Organization for Migration (IOM).
Libya has been largely lawless since the toppling of Muammar Gaddafi four years ago, and criminal gangs send vessels to carry migrants from Africa and the Middle East.
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