At least 59 people drowned after a migrant boat sank off the Greek coast in the early hours of Wednesday, that country's Coast Guard said.

No one on board the fishing boat was wearing a life jacket, the Coast Guard said. A total of 104 migrants who were traveling on the boat have since been rescued from the water and transferred to the city of Kalamata.

It remains unclear how many people were on board the ship when it went under. State broadcaster ERT, citing initial information from authorities, said the boat had sailed from Tobruk, in Libya.

Ongoing search and rescue operations are being carried out by the Coast Guard in international waters, 47 nautical miles off the coast of Pylos in the southwestern Peloponnese.

The boat's destination was Italy, according to Greek officials.

Greece has been at the heart of the European migrant crisis, offering a way into the European Union for migrants and refugees coming from the Middle East, Asia and Africa.

The number of undocumented people arriving on European shores by sea has skyrocketed this year due to conflict, global inequality and the climate crisis.

More than 36,000 people arrived in the Mediterranean region of Europe from January to March this year, nearly twice the number compared with the same period in 2022, according to figures from the UN's refugee agency (UNHCR).

It is the highest number since the refugee crisis that peaked in 2015 and early 2016 -- during some of the fiercest fighting in Syria's civil war -- when the arrival of more than 1 million people on Europe's shores led EU solidarity to collapse into bickering and border chaos.