Thousands of refugees stuck on the Turkey-Greece border clashed with Greek police on Saturday.
Greek police fired tear gas at refugees who have amassed at a border crossing in the western Turkish province of Edirne, some of whom responded by hurling stones at the officers.
The clashes come as Greece bolsters its border after Ankara said it would no longer prevent refugees from crossing into Europe following the death of 33 Turkish troops in northern Syria.
A group of Afghans with young children waded across fast-moving waters of the Evros river and took refuge in a small chapel. They crossed into Greece on Friday morning.
"Today is good" said Shir Agha, 30 in broken English. "Before, Erdogan people, police problem," he said. Their shoes were caked in mud. It had rained heavily the night before, and by early morning, temperatures were close to freezing.
Turkish President Recep Tayyip Erdogan on Saturday vowed to allow refugees to travel on to Europe from Turkey which he said can no longer handle new waves of people fleeing war-torn Syria.
Hungary has also moved to strengthen its southern border in reaction to the move.
Prime Minister Viktor Orban said Hungary would strengthen the protection of its frontier after Mr Erdogan informed him that Turkey could no longer hold back the flow of refugees.
"During a phone call earlier today on migration and the current war situation in Syria, Turkish President Recep Tayyip Erdogan informed PM Orban that there is enormous pressure on Turkey and that they can no longer hold back the flow of migrants," the government's press office said in a statement late on Friday.
Mr Orban convened a meeting of his security cabinet which decided that "Hungary must strengthen the protection of its borders and pay special attention to developments on the Balkan migration route."
Refugees in Turkey headed towards European Union frontiers on Friday after an official said the borders had been thrown open, a response to the escalating war in Syria after the killing of the Turkish soldiers.
The EU said that Ankara had made no formal announcement of any change in policy at the border.
Nato envoys held emergency talks at the request of Turkey, a Nato member. Turkey's 28 allies also expressed their condolences over the deaths and urged de-escalation, but no additional Nato support was offered.
Apart from providing some aerial surveillance over Syria, Nato plays no direct role in the conflict. But its members are deeply divided over Turkey's actions there, and European allies are concerned about any new wave of refugees.
Mr Erdogan, whose country already hosts more than 3.5 million Syrian refugees, has long threatened to "open the gates" for millions to flee to Europe unless more international support was provided.
One of the most vociferous opponents of Muslim immigration into Europe, Hungary's Mr Orban won a third term in power in 2018. During the peak of the refugee crisis in 2015, he had effectively sealed Hungary's southern border with a fence. Hungary was a transit route for hundreds of thousands of migrants heading through the Balkans to western Europe.
Turkey's neighbours Greece and Bulgaria, both EU member states, vowed not to admit the refugees and reinforced their borders following Ankara's threat to reopen the frontier.
It was closed under an accord between Turkey and the EU that halted the 2015-16 refugee crisis when more than a million people crossed into Europe by foot.
Back on the border with Greece, the authorities repulsed efforts by more than 4,000 people to enter from Turkey, according to Greek government spokesman Stelios Petsas. He said 66 people who managed to cross were arrested, and "they had nothing to do with Syria's Idlib".
Ali Nikad, a 17-year-old Iranian who made it into Greece overnight with a group of friends, said he'd spent two months in Turkey but couldn't make ends meet, and was hoping to find his uncle who was already in Greece.
"We learned the border was open and we headed there. But we saw it was closed, and we found a hole in the fence and went through it," Mr Nikad said.
Inside Syria, there was ample evidence of the renewed fighting that has caused perhaps the worst humanitarian crisis of the conflict.
A million civilians have been displaced since December inside Syria near the Turkish border in desperate winter conditions. Turkey, already home to millions of Syrian refugees, says it cannot take any more.