At least 13 migrants have died after their dinghy and a ferry collided off Turkey, the coastguard there says.
The accident happened close to the port of Canakkale. The boat was reportedly on its way to the Greek island of Lesbos.
The coastguard said eight people were rescued, with one seriously injured, and the operation is ongoing.
Meanwhile tens of thousands of migrants continue to cross Balkan borders, many of them now passing into Austria.
Long queues of both people and traffic have been reported at Slovenia's borders with Croatia and Austria amid tighter restrictions.
Austria, Hungary and Croatia have all accused each other of failing to deal effectively with the new arrivals.
Turkey's coastguard said it raised the alarm after being told that a commercial vessel and a migrant boat had collided off Canakkale.
It is believed to be the second migrant boat to have sunk between Turkey and Greece on Sunday (20/9).
In the other incident, Greece's coastguard said it had rescued 20 people spotted in the water near the island of Lesbos - a further 26 people are feared to be missing.
On Saturday, a five-year-old girl died and 13 people were left missing after their boat also sank off Lesbos.