Greek authorities recovered 12 bodies from a boat carrying migrants off the southern coast of Crete early on Monday, in the latest deadly crossing on the sea route from Libya to Greece.

The coast guard said the boat was found about 15 nautical miles off Kaloi Limenes, a small port on the south of the island. Eighteen people were rescued from the vessel by a Moroccan-flagged cargo ship that was sailing nearby, and a search operation was launched in the surrounding waters.

The cause of death and the identities of those who died have not yet been established, and it is not yet clear how many people were on board when the boat got into difficulty.

Two more boats found in the same area

In a separate development on the same stretch of sea, a Frontex aircraft and a drone spotted two other boats carrying migrants. One was carrying around 47 people and the other around 40, and everyone on board both vessels was rescued.

The three incidents underline how busy the crossing from Libya to Crete has become. Greece's migration minister, Thanos Plevris, has said about 1,700 people arrived from Libya in the first three days of November alone.

A second deadly incident

Kaloi Limenes, whose name means "good harbours", is a small fishing village on Crete's south coast, about 75 kilometres southwest of Heraklion. Its sheltered bay has long been used by local fishermen, and it now sits on one of the busiest stretches of sea for boats crossing from North Africa.

Frontex, the European Union's border agency, supports Greek search-and-rescue operations in the area with aircraft and drones, and it was one of its aircraft that spotted the two additional boats on Monday.

The deaths off Kaloi Limenes follow a separate operation in which eight people died and 28 were rescued after their boat got into trouble, with the tug Pyrros involved in the rescue. The two incidents are distinct, and the authorities have not linked them.

Crete has become one of the main destinations for boats leaving Libya. The crossing is long and exposed, and the boats used are often unseaworthy and overloaded, leaving little margin when the weather turns or an engine fails.

Monday's deaths are the latest in a series of fatal incidents on the Mediterranean's central routes this year, where overcrowded boats regularly get into difficulty far from shore and far from help.

Greek officials have repeatedly warned that the route is dangerous, particularly as winter approaches and conditions in the Mediterranean deteriorate. Rescue operations in the area are complicated by the distance from shore and the volume of traffic.

Further details about the survivors and the dead have not yet been released.

Sources: Reuters; Associated Press.