A drowned two-year-old boy became the first known migrant casualty of the year on Saturday after the crowded dinghy he was travelling in slammed into rocks off Greece's Agathonisi island, the coastguard said.

The other 39 passengers, including a woman who had fallen overboard, were rescued after local fishermen raised the alarm. Ten of the survivors were taken to hospital to be treated for hypothermia. The rubber vessel had set off from Turkey in the early morning in windy weather.

The charity Migrant Offshore Aid Station (MOAS), which helps save migrants and refugees at sea, deployed its fast-rescue Responder boat to help bring the stranded passengers to safety in a joint operation with the Hellenic coastguard.

The toddler's body was pulled out of the water by fishermen, according to the coastguard. The migrants, including the child's mother, were taken to the port of Pythagorio on Samos, the nearest island, which is 50 kilometres away.

There was no immediate information about their nationalities. "Nothing can prepare you for the horrific reality of what is going on. Today we came face to face with one of the youngest victims of this ongoing refugee crisis. It is a tragic reminder of the thousands of people who have died trying to reach safety in miserable conditions," said MOAS founder and US entrepreneur Christopher Catrambone in a statement.

Three-year-old Syrian toddler Aylan Kurdi, whose limp body was photographed washed up on a Turkish beach in September, became a heartbreaking symbol of the refugee crisis.

Meanwhile, Turkish coastguards rescued 57 migrants seeking to reach EU member Greece by sea after they were stranded on a rocky islet in the Aegean Sea, official media said yesterday.

The migrants were trying to reach the Greek island of Lesbos but their boat hit trouble after leaving the resort of Dikili in Izmir province on Turkey's Aegean coast.