ATHENS, Jan 28 – Twenty-four migrants drowned when their boat sank off a Greek island close to Turkey, the Greek coastguard said, as people continue to risk the crossing to Europe despite harsh winter conditions.

"We have 10 rescued and 11 missing," a coastguard official said on Thursday. "The search and rescue effort is continuing."

The sinking occurred late on Wednesday north of the island of Samos in the eastern Aegean Sea, close to the Turkish coast.

The coastguard said a man who managed to swim ashore told Greek authorities the boat had been carrying 40 to 45 people.

Coastguard vessels and a helicopter were continuing to look for survivors.

More than 600,000 migrants fleeing Syria, Afghanistan and other war-torn or impoverished countries arrived in Greece from Turkey last year, risking the short but dangerous sea crossing, often on inflatable rafts. Hundreds have drowned.

Six migrants including a child drowned when their vessel sank off the island of Kos close to Turkey early on Wednesday.

EU countries have been increasingly critical of Athens' handling of the continent's worst migration crisis since World War Two. More than a million migrants reached Europe last year, mainly through Greece.

On Wednesday, the European Commission warned there could be more controls over movement between Greece and other states in the free-travel Schengen zone from May unless it fixed "serious deficiencies" in its management of the zone's external frontier.