At least 45 people including 20 children, have died after their boats sank on their way from Turkey to Greece on Friday, with dozens of others reported missing, coastguard officials in Greece and Turkey said.

The Greek coastguard said it had rescued 74 people after two boats ran into trouble off the Greek Aegean islands of Farmakonisi and Kalolimnos in the early hours.

A search operation was under way for dozens of people still missing from the boat that capsized off Kalolimnos.

Separately, the Turkish coastguard said it had found the bodies of three children on Friday after a third boat sank near Didim, the Dogan news agency reported. The coastguard was searching for others.

Helicopters from EU border agency Frontex were also involved in the searches.

People fleeing war and misery in the Middle East and elsewhere - many of them Syrian refugees - are still arriving in their thousands in Greece from Turkey in flimsy boats.

The International Organisation for Migration estimates that about 31,000 people have reached Greece by sea so far this year.

The IOM reported 77 people died trying to cross the Mediterranean between January 1 and January 17.

On Thursday at least 12 people, including children, drowned off the Turkish coast as their boat tried to reach Greece. The Turkish coastguard rescued 28 others.

A five-year-old and two women died from hypothermia on the Greek island of Lesbos on Wednesday after crossing from Turkey in freezing weather, Red Cross officials said.

More than 18 boats, each carrying up to 45 migrants, washed up on the island’s beaches on Wednesday.

The UN refugee agency said smugglers were offering desperate migrants discounts to lure them out.

"Newly arriving refugees told UNHCR that the smuggling rates had halved in recent days. This discount acts as a grim enticement to take extraordinary risks given worsening weather," the agency said.

Turkey, which is home to some 2.2 million refugees from Syria's civil war, has become a hub for migrants seeking to reach Europe, many of whom pay people smugglers thousands of dollars for the risky crossing.

Ankara reached an agreement with the EU in November to stem the flow of refugees heading to Europe, in return for financial assistance.

Brussels vowed to provide $3.3bn as well as political concessions to Ankara in return for its cooperation in tackling Europe's worst migrant crisis since World War II.

German Chancellor Angela Merkel - whose country took in 1.1 million asylum seekers in 2015 - was set to meet Turkish Prime Minister Ahmet Davutoglu on Friday, with the migrant crisis top of the agenda.

The outcome of the talks is not only important for Merkel, who faces intense pressure at home to impose a cap on Germany's refugee intake, but will also have resonance across Europe where public opinion is hardening against the record asylum seeker influx.

The fresh deaths came as the French Prime Minister, Manuel Valls, warned on Friday that Europe risks becoming "completely destabilised" as a result of the current migrant influx.

Speaking to the BBC, Valls said that "if Europe is not capable of protecting its own borders, it's the very idea of Europe that will be questioned".