At least 33 refugees drowned off Turkey's Aegean coast as they tried to reach a Greek island, and a search and rescue operation was under way for the remaining passengers.

Turkey's private Dogan News Agency, which reported the 33 deaths on Monday, said that one boat set sail from Turkey's Edremit coastal district and the other from the town of Dikili, further south.

Both were headed for the Greek island of Lesbos, just a few kilometres away.

One refugee was rescued by a fisherman and three more were rescued by the coastguard, which said it had deployed boats and helicopters to search for 13 more passengers.

A coastguard official told Reuters the death toll was lower, at 22.

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Monday's deaths came as Turkish and German officials held talks to stem the flow of refugees bound for Europe.

The deaths also came as tens of thousands of Syrians remain stranded at the border with Turkey after fleeing a Russia-backed government offensive in Aleppo.

More than 900,000 people fleeing Syria, Afghanistan and other war-torn or impoverished countries arrived in Greece from Turkey last year, often risking their lives in the short but perilous sea crossing in overloaded boats.

Last month marked the deadliest January on record for refugees trying to reach Europe, as more than 250 died while making the journey.