At least 25 migrants including children died on Sunday when their wooden boat capsized in the Aegean Sea while trying to cross from Turkey to Greece, the Turkish coastguard said.

Fifteen migrants were rescued following the capsizal off the coastal town of Didim in southwest Turkey. Ten out of 25 dead were children.

Contacted by AFP, a Turkish official, who previously put the toll at 18, confirmed the latest figure, saying the coastguard had found seven more bodies.

The nationality of the migrants was not immediately known.

The coastguard, backed up by three boats and one helicopter, was still searching for more survivors, it said.

The tragedy comes a day before a crucial summit between Turkey and European Union leaders in Brussels.

Turkey is the main launch pad for most of the more than one million refugees and migrants who have crossed into Europe since early 2015 and under is pressure to curb the huge flow.

The 28-nation bloc is hoping for new commitments from Turkish Prime Minister Ahmet Davutoglu at their talks in Brussels in order to stop the stream of refugees.

In an official visit to Ankara this week, EU President Donald Tusk said the number of migrants crossing the Aegean Sea from Turkey to EU territory remained "far too high".