Some 700 African migrants are feared dead on Sunday, after their boat capsized off the coast of Libya in the Mediterranean Sea. 

Declared an emergency at around midnight, the ship is believed to have started capsizing when migrants aboard all moved to one side of the ship, as a merchant vessel approached. 

Only twenty-eight people have been rescued so far from the site of the capsized ship, which occurred just out of Libyan waters, or 120 miles south of Italian island Lampedusa. 

“At the moment, we fear that this is a tragedy of really vast proportions,” Carlotta Sami, a spokeswoman for the United Nations High Commissioner for Refugees, told SkyTG24 television.

If scale of the disaster is confirmed, it would be one of the worse incidents seen in the decades-long African migrant crisis in the southern Mediterranean. 

Along with those killed in other similar scenarios since the beginning of 2015, the 700 people believed dead in this crisis would raise the number of casualties to more than 1,500. 

Just last week, some 400 African migrants were presumed dead in another ship sinking off the Libyan coast.