A major search-and-rescue operation was underway Sunday night after a migrant boat carrying 77 people capsized and sank about 38 nautical miles south of Gavdos, Greece's southernmost inhabited island, Greek authorities and local media reported.

Authorities said 52 people had been rescued, while approximately 25 remained missing. One person was found unconscious during the operation, according to reports. Earlier Greek media reports put the number rescued at 51 before the figure was updated.

The operation was being coordinated by Greece's Joint Search and Rescue Coordination Center (EKSED), with several Greek Coast Guard vessels, Frontex vessels and aircraft involved. A Greek Air Force helicopter and a Frontex unmanned aerial vehicle were also deployed to search the area for survivors.

According to accounts from survivors, 77 people had been aboard the boat before it capsized. The vessel was subsequently reported to have partially sunk, leaving rescuers searching a wide area of the Libyan Sea for those still unaccounted for.

The nationalities of the passengers and the exact type of boat involved had not immediately been disclosed by Greek authorities.

The incident occurred amid a continuing increase in migrant crossings on the sea route from North Africa toward Crete and Gavdos. The waters south of Gavdos have become a major maritime corridor for people attempting to reach Greece from Libya.

In August, Greek authorities carried out two separate rescue operations south of Gavdos in which about 131 migrants were rescued from three boats, according to reports. A Frontex drone detected the vessels before Frontex ships moved in to rescue the passengers.

Earlier in June, Frontex vessels also rescued 70 migrants in two separate operations south of Gavdos, highlighting the sustained pressure on the route.

The latest shipwreck underscores the dangers faced by migrants attempting the Mediterranean crossing in overcrowded and often unseaworthy boats. Search teams continued working through the night in an effort to locate the missing passengers.

The number of people missing remained subject to change as authorities continued to verify survivor accounts and assess the situation at sea. (ILKHA)