At least three people have drowned and the Greek coastguard has rescued over 240 others after a wooden boat carrying migrants and refugees sank off the coast of Lesbos, authorities have said.

The Greek coastguard searches for those missing in the Aegean Sea. Credit: Reuters

Three passengers - a two young boys and a man - were found drowned and an extensive search is underway, the Reuters news agency reports.

A volunteer escorts a rescued girl after the sinking. Credit: Reuters

Authorities on the Greek island do not yet know how many people may be missing.

Video from the Associated Press shows a fishing boat arrive in port, her decks full of men, women and children rescued from the stricken vessel.

Medics and volunteers greet the shocked migrants at the harbour wall, and administer blankets and first aid.

Lesbos lies less than 10 kilometres (6 miles) from the Turkish coast in the Aegean Sea and is now seen as the main route for the many thousands of people from the Middle East and Africa hoping to reach safety and prosperity in the European Union this year.

A volunteer carries a rescued child. Credit: Reuters

Over 500,000 people have entered Greece via its outlying islands in 2015, in what has arguably become the greatest humanitarian crisis to hit Europe since the Second World War.