Greek authorities on May 24 began to gradually evacuate Idomeni, the country's largest refugee camp, on the Macedonian border.
At least 200 riot police started blocking access to the area, but the government's spokesman for the refugee crisis, Giorgos Kyritsis, said police would not use force.
He said the operation would last a week to 10 days.
The camp is home to an estimated 8,400 people. Authorities said the residents will be moved gradually to newly completed, organized camps.
Journalists were barred from the Idomeni camp. Buses carrying riot police units were seen heading to the area, accompanied by a helicopter.
More than 54,000 refugees and migrants have been trapped in financially struggling Greece since Balkan and European countries shut their borders to a massive flow of more than 1 million people who came through last year trying to escape war and poverty at home.
The vast majority of the migrants are from Syria, Iraq, and Afghanistan and most arrived by boat from nearby Turkey.
Today, they face deportation back to Turkey unless they successfully apply for asylum in Greece.