Thousands of migrants stuck on the Turkey-Greece border have clashed with Greek police.

Greek police fired tear gas at people 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. 

Turkish president Recep Tayyip Erdogan vowed to allow refugees to travel on to Europe from Turkey.

"What did we do yesterday? We opened the doors," Mr Erdogan said in Istanbul in his first comments since the deaths of the Turkish troops on Thursday.

"We will not close those doors ...Why? Because the European Union should keep its promises." 

The Turkish leader also said 18,000 migrants have amassed on the Turkish borders with Europe since yesterday, adding that the number could reach as many as 30,000 today.