LESBOS, Greece - Greece says it has stopped nearly 10,000 migrants crossing over the land border from Turkey.
Separately, Greek police say at least 500 people on seven boats have reached the Greek islands of Lesbos, Samos and Chios, where camps for migrants are already severely overcrowded.
Turkey has vowed to open its doors for migrants to travel to the EU.
Turkish President Recep Tayyip Erdogan says it cannot deal with the amount of people fleeing Syria's civil war.
His decision came after at least 33 Turkish soldiers were killed in air strikes in Idlib province in northern Syria this week.
Greek Prime Minister Kyriakos Mitsotakis has called a meeting for his country's national security council later on Sunday.
The EU's border protection agency Frontex said it was on "high alert" on Europe's borders with Turkey.
Turkey is hosting 3.7 million Syrian refugees, as well as migrants from other countries such as Afghanistan - but had previously stopped them from leaving for Europe under an aid-linked deal with the EU.
But Mr Erdogan accused the EU of breaking promises made in 2016, when Ankara agreed to help shore up the EU's south-western border.
Almost 10,000 migrants have been blocked from entering Greece in the last day, the Greek government has said.
Some migrants tossed stones, metal bars and tear gas canisters when stopped at the border.(FA)