A group of migrants have tried to bring down a fence in a bid to break through into Greece, while others hurled rocks at Greek police during ugly scenes at the border with Turkey.
Greek authorities responded by firing volleys of tear gas at the youths.
At least two migrants were injured in the latest clash between Greek police and migrants gathered on the Turkish side of a border crossing near the Greek village of Kastanies.
As in previous confrontations this week, officers in Greece fired tear gas to impede the crowd, before Turkish police fired tear gas back at their Greek counterparts.
A Greek government official said the tear gas and water cannon were used for “deterrence” purposes.
Thousands of migrants have headed for Turkey’s land border with Greece after Turkish president Recep Tayyip Erdogan’s government said last week that it would no longer prevent migrants and refugees from crossing over to European Union territory.
Greece deployed riot police and border guards to repel people trying to enter the country from the sea or by land.
Mr Erdogan plans to be in Brussels on Monday for a one-day working visit.
The announcement came hours after EU foreign ministers meeting in Croatia on Friday criticised Turkey, saying it was using the migrants’ desperation for political purposes.
The Greek government said that around 600 people, aided by Turkish army and military police, threw tear gas at the Greek side of the border overnight.
The government statement said: “Attempts at illegal entry into Greek territory were prevented by Greek forces, which repaired the fence and used sirens and loudspeakers.”
Thousands of migrants have slept in makeshift camps near the border since the Turkish government said they were free to go, waiting for the opportunity to cut over to Greece.
Mr Erdogan announced last week that Turkey, which already houses more than 3.5 million Syrian refugees, would no longer be Europe’s gatekeeper and declared that its previously guarded borders with Europe are now open.
The move alarmed EU countries, which are still dealing with the political fallout from a wave of mass migration five years ago.
Mr Erdogan has demanded that Europe shoulder more of the burden of caring for refugees. But the EU insists it is abiding by a 2016 deal in which it gave Turkey billions in refugee aid in return for keeping Europe-bound asylum-seekers in Turkey.
While crediting Turkey for hosting millions of migrants and refugees, European foreign ministers said the bloc “strongly rejects Turkey’s use of migratory pressure for political purposes”.
They called the situation at the border unacceptable and said the EU was determined to protect its external boundaries.
In Berlin on Saturday, about 1,000 people rallied in front of the interior ministry urging Germany to take in asylum seekers stuck at the Greek border. They then marched through the streets downtown behind a banner reading “Europe, don’t kill. Open the borders, we have space.”
Greek authorities said they thwarted more than 38,000 attempted border crossings in the past week and arrested 268 people — only 4% of them Syrians. They reported reported 27 more arrests on Saturday, mostly migrants from Afghanistan and Pakistan.
Greece has described the situation as a threat to its national security and has suspended asylum applications for a month, saying it will deport new arrivals without registering them.
Many migrants have reported crossing into Greece, being beaten by Greek authorities and summarily forced back into Turkey.
