Greece's coast guard says at least 11 people, most of them children, have died in the latest migrant boat sinking off an eastern Greek island.

The circumstances of Thursday's sinking were unclear. The Greek coast guard and vessels from the European border patrol agency Frontex were carrying out a search and rescue operation off the island of Samos. Ten people were rescued, while 11 bodies — those of four boys, three girls, three men and one woman — were recovered.

The sinking is the second in two days. Another boat sank off the island of Kos on Wednesday, leaving seven dead, including two children.

Greece, with thousands of kilometres (miles) of coastline and islands very near the Turkish coast, is the main gateway into Europe for refugees and migrants.