ATHENS - The bodies of four migrants - one boy, one girl and two women - have been recovered from a sinking boat off the Greek island of Lesbos while another 23 migrants were rescued, Greece's coastguard said on Thursday.

The boat was detected by a patrolling coastguard vessel at about 2 am (2300 GMT). A search and rescue operation was still ongoing, a coastguard official said. It was not immediately clear how many people may have been on the boat.

ALSO READ: Sources: Greek inquiry into 2023 migrant shipwreck finds coastguard breached maritime rules

Greece, in the southeast corner of the European Union, has long been a favoured gateway to Europe for migrants and refugees from the Middle East, Africa and Asia. In 2015 nearly 1 million people landed on its islands.

READ MORE: Migrant boat sinks off Greek island, 3 dead, 25 missing

Last year, about 54,000 migrants reached Greece, the second largest number in southern Europe behind Italy. The vast majority of them arrived by sea, according to data from the UN refugee agency UNHCR.