At least four migrants have died in distress at sea off the Greek island of Lesbos.

Seven other people, said to be men from Sudan, who were aboard the vessel, have been rescued, with the search for possible further missing persons ongoing, according to Greek public broadcaster ERT, citing the coastguard.

It was initially unclear how many people were on board the boat.

Strong winds have been sweeping the region, which may have contributed to the accident and hampered the search-and-rescue operation, involving several coast guard vessels, a helicopter, and search parties on land.

According to the United Nations High Commissioner for Refugees (UNHCR), more than 30,000 refugees and migrants have crossed the Mediterranean to Greece so far this year.

Most of them embark on the dangerous journey from the western coast of Turkey or from Libya.

(dpa/NAN)