Migrants and Greek police clashed along the Turkish-Greek border on Saturday.
Greek police fired tear gas at migrants who amassed at a border crossing in the Turkish state of Edirne. There were also reports of stones being hurled by refugees at the officers.
"The situation is very dramatic," said DW's Turkey correspondent Julia Hahn, who is at the border. She reported teargas or pepper spray being used by the Greek forces and said "hundreds of migrants" entered no-man's land.
"Some have tears in their eyes, are coughing, some look like they're about to faint," she said.
She witnessed people crossing under a fence into the border area.
Why are migrants trying to enter Greece now?
Greece bolstered its border security on Friday after Turkey said it would no longer prevent refugees from crossing into Europe following the killing of 33 Turkish troops in northern Syria.
"The government will do whatever it takes to protect its borders," Greek government spokesman Stelios Petsas told reporters.
On Saturday President Recep Tayyip Erdogan vowed to uphold Friday's threat to allow refugees to travel on to Europe from Turkey. He says Turkey can no longer handle new waves of people fleeing war-torn Syria.
"What did we do yesterday? We opened the doors," Erdogan said in Istanbul in his first comments since 33 Turkish troops were killed in northern Syria on Thursday. "We will not close those doors. Why? Because the European Union should keep its promises."