At least 78 people were killed and several are feared missing after a fishing boat carrying migrants sank off the coast of Greece on Tuesday, reported Reuters.

The Greek coastguard said the boat capsized in international waters, 47 nautical miles (about 87 kilometres) southwest of Pylos town, near the Peloponnese coast. The vessel had set out sail from eastern Libya for Italy, according to The Guardian. Among those killed were mostly men from Afghanistan and Pakistan.

Authorities said 104 passengers have been rescued so far. However, the number of people on board remains unknown. Media reports and humanitarian organisations estimate that there could have been between 400 to 700 people on board.

Greece serves as a major entry point to the European Union for migrants from the West Asia and Africa. While many immigrants make their way to the Greek islands from neighbouring Turkey, an increasing number of boats are embarking on a riskier and lengthier journey from Turkey to Italy via Greece, according to Reuters.

On Wednesday, the Greek coastguard said the boat had been spotted in international waters late on Tuesday by an aircraft belonging to the European border agency Frontex, reported the Associated Press. Following this, a coast guard vessel was dispatched. However, those on board refused any assistance and said that they wanted to continue their voyage. But just a few hours later, the boat capsized.