Some attempt to cut through a barbed-wire fence while others hunt for wood and rocks to toss at police, but the final goal for the thousands of migrants at the Kastanies border town between Turkey and Greece is to reach Europe. A few kilometers from the tense scenes at Kastanies, hundreds of migrants managed to enter northern Greece, crossing the Evros River which runs along the frontier for 200 km (124 miles).

"Are we in Greece?" asks a young Afghani as he walks in a group of 20 people along a provincial road near the town of Orestiada, adding: "Where can we find a taxi or a train to go to Athens?"

The Greek police have been "arresting people all the time, from early in the morning," an officer said. Most of those picked up were young men "mainly from Afghanistan," carrying no luggage.

At Kastanies, known as Pazarkule on the Turkish side, some 4,000 migrants have massed behind the fences, according to the Greek police. Twenty-four hours earlier there were 1,200. Some climb trees to get a better look at what's ahead of them, others throw chunks of concrete over to the Greek side. Some even toss teargas canisters over the barbed wire. On minor roads straddling the border, groups of refugees walk without rest. Some have lost their shoes in the river. They are covered in mud and exhausted as they suffer in the cold and rain, hoping to reach Greece's second city Thessaloniki, which is three hours trudge away, or the capital Athens, where they would seek to contact U.N. representatives for aid.

"We have been walking for four days," Shadi, a 36-year-old man from Iran, told Agence France-Presse (AFP) wearily. "We have crossed the river... I want to reach Albania and from there to go to Europe," he adds as he marches near the village of Neo Cheimonio, about 5 km west of the Turkish border. He was traveling with a group of Afghan and African men, with only the drenched clothes they are standing in.

In the Greek village of Marassia, near the river, cafe owner Popi Katrivezi has never seen anything like it, telling AFP: "We are used in such situations these last years, but never anything like what has happened since Friday. It seems like thousands are coming in from Turkey."

Just a few meters away, some Afghan families, including five children, have found shelter in a chapel. Worn out and hungry, they beg for food and water, imploring reporters for help.

Turkey opened its borders to Europe amid a military escalation in northwestern Syria’s Idlib province that has forced hundreds of thousands of Syrian civilians to flee advancing Bashar Assad regime forces backed by Russia.

“We can’t handle a new wave of migration,” President Recep Tayyip Erdoğan said Saturday, in an apparent reference to the growing humanitarian crisis in Idlib. Nearly 950,000 displaced civilians have been pushed toward the Syrian-Turkish border amid cold winter weather.

Erdoğan said Turkey would not stand in the way of refugees and migrants already in the country who hope to head to Europe.