A witness on board the Antigua and Barbuda-flagged cargo ship said they saw one person swimming away from the yacht, but gale force winds in the area were hampering any further search and rescue operations Wednesday morning, the coast guard said.
It said the cargo ship was transporting the migrants to Turkey.
Thousands of people fleeing war or poverty in the Middle East, Africa and Asia arrive on Greek islands each year in an attempt to make their way into the European Union. Most make their way to islands near the Turkish coast in small inflatable dinghies. But Greek authorities have said they have noticed a recent trend of smugglers using larger vessels — yachts or sailboats — to ferry people to Italy.